This testing was done using fastest settings, and normal fleet size. 
This is an assessment of combat capability of two races when facing each other, advent vs vasari.
Considering everyone is gaining resources at the same rate, an analysis of mass cost vs military effectiveness will occur using total economic cost with a lot of practical battle experience added in to keep the rediculous battle math out of the convo so that this will be easily read by all.
Everyone with even a little experience of the game understands the awesome capability of the vasari starbase vs the other starbases, and fundamentally this is the core of the problem with the advent vs. vasari matchup. 

a 30 illuminator fleet is a nice round number that is about where you get an effective number of illuminators to focus fire capital ships, if maneuvered properly.  this is also strong enough to take out a weak unupgraded starbase that hasn't began a health upgrade, so it is quite useful for the advent to attain this fleet.  Smart players won't want to attack this size of an illum fleet without spending cash on additional fleet capabilities above and beyond straight unit spam.  They will invest in upgrades and build some new ships to counter.  If they face the illuminators early on usually they will get cut to pieces, if done properly.
Advent need a sizeable fleet to attack the enemy, as their capital ships have the least amount of staying power
in a fight which puts them at an overall disadvantage.

This fleet will be matched with the vasari early game counter to efficient advent fleet spam of a defensive starbase at the vasari homeworld.  This assumes some close quarters combat, and this often occurs in large multiplayer games, about 2-3 jumps from homeworld to homeworld. The closer the races are to each other, the more important capital ship starting choice becomes(in the case of the sova, it becomes game breaking).  Note: you have to spam a decent number of disciples and scouts to force a vasari player to go on the early defensive, and these costs are not reflected in this discussion because how many ships produced to get the desired effect depends entirely upon the player you are facing.

11400 creds, 1800 metal, and 1650 crystal would be needed to build your 30 ship illum fleet up and functional(not counting research costs).  Total costs of research would be 3050 creds, 340 metal, and 415 crystal(3 labs + the cost of the illum research).  Total base time of production for the illuminator using one factory would be 630 seconds (10.5 min).
You start with 2 constructors so you can build two labs immediately at the same time, so the time for only two of the three
labs would be used as a time factor for the "fastest possible construction time". This would be 108 seconds, + the time of the research which would be 161 seconds.

So, currently the total cost of 30 illuminators built from one factory would be 14850 credits, 2140 metal, and 2090 crystal,
in 13.1833 minutes to achieve the fastest production of illuminators possible. This blatant strategy would be easily discovered by the first wave of scouting and the enemy upon first glance will start countering you most likely by building flak or even more fun, building a starbase to protect your gravity well forever. I am going to show the relatively huge price range disparity between the cost of purchasing effective capability of the vasari starbase put in an enemy grav well vs building a strong enough counter to take it out. 
This is the maximum speed at which the advent could spam using one factory. 
Naturally more factories could be used, but I didn't factor them in to keep total costs as low as possible to show everyone advent's maximum capability for minimum cost. 
This will become quite important later on when we factor in the vasari maximum capability, as I am trying to show how not overpowered the vasari are using this method to stop the hate that the heavily pro vasari players will throw at me in this forum. A 600 credit, 80 metal, 80 crystal factory would cut about 5 minutes off of this 13 minute time, and is well worth the investment. You have to procure more logistics slots though, and therefore the advent accrue additional costs for that extra slot by either paying for an asteroid or upgrading the homeworld logistics slot.
(something the vasari don't have to actually pay for to get the relatively similar capability).

2 vasari carriers, cost 4600 credits, 400 metal, and 350 crystal, . 
1 starbase built an an enemy grav well without upgrades costs 3600 credits, 500 metal, and 475 crystal.
with one health upgrade and one weapon upgrade the vasari have a potent force in the beginning of the game able to attack or defend effectively.2 vasari starbase upgrades: 3600 credits, 550 metal, and 300 crystal.combined, the total cost is  11800 credits, 1450 metal, 1125 crystal.

Ship construction for two capitals takes up about 2 min(at maximum capability),
and the two military labs + research (again remembering the two constructors) takes 101 seconds.
if speed is more important, say in an attack, the vasari can send the constructor and the starbase for the enemy homeworld in about 1 minute into the game.If you don't have a STRONG counter to the starbase in your gravity well as advent already developed, you will lose to the vasari.Most players online know this so they will build up a strong fleet as fast as they can as advent to prevent this from happening.Noobs however are very vulnerable to this rush and they find it quite discouraging.

The advent would not be able to attack you and win playing perfectly with illuminators at the vasari homeworld,
and by building 2 repair structures and add only 1200 credits, 200 metal, and 175 crystal to your cost...
You still have plenty of economic room to defend against advent attack, without owning a single neutral.  When vasari own one neutral or more, early on, the economic disparity between advent and vasari starts to become quite large, and vasari gain the ability to just strong arm the advent fleet by fighting a war of attrition at the advent homeworld that they will eventually win. This is a low skill battle that is quite frustrating because it is entirely based upon luck, how many neutrals and where are randomized in common random maps.

The vasari starbase's ability to move is what grants it the unparallelled advantage against other races,
because they can build a cost effective fleet anywhere their colonizers can warp to.  This makes their colonizers an extra target in battles allowing the vasari fleet to mitigate a lot of damage per second by just warping these primary targets into the grav well.  Its a straight trade of 425 credits, 140 metal, 50 credit cost that will give your enemy more target priorities while their single target priority (your halcyon) will remain in constant danger. Add on top of that they can position starbase constructors anywhere in the grav well, so if one potential starbase construction is destroyed by enemy dps, a constructor could start constructing at the other end of the grav well which would mean that the enemy fleet would have to cross that distance under fire to take out that starbase which could at any point in time be cancelled to retrieve its resource cost, in essence getting an even cheaper form of damage mitigation. I am all for developers increasing the cost of the vasari colonizers so that this cheap form of endgame mitigation is no longer exploited.  Somewhere in the neighborhood of having a vasari colonizer cost about 1500 credits, 400 metal, and 150 crystal. This would make them a target and vasari players would have to play more conservatively with them.   
I would add that the vasari should not maintain their monopoly on effective movement in this game,
that the TEC and advent starbases should have free movement capabilities as well,
just not as fast. In this way the vasari starbase would always be able to take out the enemy starbases if it is fully upgraded,by itself and provide the necessary building destroyer the vasari only sorta need.  I say the vasari only sorta need the vasari starbase as a building destroyer, because their endgame phase missiles on their bombers will punch through starbases easily enough.

With enough resources the vasari can get this starbase defense(1 weapon upgrade, 1 health upgrade) up in 2 min 17 seconds in their grav well using fastest settings.  That is the fastest and most effective early game defense in the game.
Naturally you don't have that many resources early on to build this dream defense that quickly, but it helps to know the maximum capability of the vasari military because in multiplayer the vasari can get an early feed that will allow them to maximize their capability at any point.

I believe I have clearly proven that advent should not attack vasari early on, considering that the vasari
can build an upgraded starbase faster then the advent can spam 30 illuminators.  If you don't trust my extensive battle expertise, then just fight the battles out themselves and prove me wrong.  Make sure you play against a HUMAN player of great experience who doesn't know that you are in fact, testing them.  All those are very important factors to having a successful test.

I will not go into combat calculation, as the math doesn't take into account all the variables of position, timing etc that
only experience can really provide.  It is a waste of time. Sorry if i broke a few math loving hearts with those "harsh" words.
Looking at things from the perspective of military effectiveness, this vasari defense vs advent offense is extremely powerful,
cost efficient, quick to redoubt the defense(upgrading the vasari starbase), that the advent can try to attack the vasari early but they will always have an incredible defensive option to counter whatever the advent have to throw at the vasari.

Experienced players know this so they quickly go on the attack since their racial resource efficiency advantage allows them to do so. Given a little luck and timing, the vasari can get a starbase built in an enemy advent gravity well and have it sufficient strength to deal with the advent fleet when it arrives. If this happens, whether some unlucky positioning when the starbase is built, or no warning at all that a starbase is being built on your homeworld, the advent player should immediately think about setting up a new homeworld somewhere else. In my opinion, all planets should have an audio warning system indicating when an enemy starbase starts constructing at your planets so that
you can start countering as fast as possible.  The fact that this isn't in game indicates a lack of foresight by developers and I would also think a certain amount of racial favoritism as well.  After all the devs have caved to the vasari players once, wasn't that hard.  But to get an advent upgrade, now that is like pulling hens teeth.  The TEC are more even with the advent resource/time wise with the exception of the crippling sova ability embargo(its like the TEC I win vs advent button). 
 
So 30 illums + a halcyon, facing a substantially less expensive defense of an upgraded starbase and 2 carriers,
will not succeed in attack vs a vasari starbase in the early game. Inexperienced players might try to do this anyways,
but in the end it is an utter waste of fleet.  Vasari can effectively hold out against 2v1 this defense is so powerful.
 
Advent also have terrible building destruction capabilities with their starfish, and are by far the most inefficient building destroyers in the game. TEC are the most efficient, and vasari are somewhere in between, as their advantage also has to be balanced with the incredible defensive advantage of getting starbases on their worlds. 

So, we have learned that the vasari do not have to worry about advent illum attack in the early game if they build a defensive starbase (and most often do to counter close quarters advent tier 0 spam), which can be defeated by an early vas weapon upgrade, where the starbase will survive with about 5% health, usually).  Since the advent fleet does almost as poor as the vasari fleet when factoring in attrition (costs of ships are far closer to each other then that of TEC and vasari, or TEC and advent) Every ship lost is major.  This creates exciting game play but does not in any way change the long term inevitability of the match up, vasari starbases kill an effective amount of advent ships until the late late endgame.  The vasari get a far more capable, far more mobile fleet that will crush the advent before they reach their eventual awesome fleet.  Even if the advent eventually do, I would say that the vasari fleet is stronger because of the multiple target
options provided by their starbase constructors, again money for mitigation.  So the vasari have all their bases covered, and on average they are the strongest race if they are smart enough to avoid early attrition, use starbases, and keep their precious neturals in their cold icy claws.


So, why play advent if you are already down for the count at the start of the game?
Advent help to improve your skills(you have to play perfect to have a chance to win),
and give you serious bragging rights when you defeat people with them of course!!!

truly if you do upgrade advent I will become a very strong force in the game,
but no worries i've gone to the darkside and am currently ironing out the kinks in my vasari game so that I can be just as OP as everyone else.
What fun!