I completely agree! Love everything about GC2/3 but the end game tends to get monotonous. The Dread Lords have been extremely disappointing for me. Not once have they ever been a significant challenge. either the AI kills them off before I even meet them or they spawn right near me and are killed off in a few turns... In GC2 I was always scared of them and they became my #1 priority, and still do, but they are never something to be feared in this iteration. Hoping that will change and that they come up with some more interesting stuff for the end game. Have no idea about Stellaris but it sounds good.

I play on medium - large. Anything bigger and by the time I get around to dealing with the other side of the map, everyone's researched all techs and its just battle of the gods.

GC2 had these events that come up late game.  The Jagged Knife is an infamous and (for me)unpopular example.  The ambassador incident that suddenly triggers war is another.  I expect we will see something like that sooner or later in GC3.  Brad has acknowledged the issue and pretty much hates it as much as we do.  The fan response to the late game events can be mixed, so I am sure they are trying to be judicious about what monkey wrenches they will be throwing into our late games.  

However, it is my ardent hope that the AI will get more and more clever about strategic Diplomacy and late games turn into alliances and escalations and complications, with warfare, treaties, embargoes and backstabbing.  I want playing against multiple factions to be exponentially more difficult as the number of opponents grows.  10 enemies is much more dangerous than 2.  A hundred enemies should be monumental.  The consequences and instability would snowball as the game progressed.  It is possible this would dovetail with espionage plans also. If they adopt those kinds of behaviors, your late games should never be dull again.

Well i don't think they needed to get rid of the kagged knife they just needed to fix it. The jagged knife needed to fix it's ecenomy. Needed to be able to destroy and fix stuff. 

Yes, good that the AI found a way to push me back from 76% to 74% influence. Perhaps that was intentional on their parts or perhaps it just was a normal part of their building up those planets. Anyhow, the next time, I'll make sure to plant a few more cultural influence SB's near the borders or I'll simply send in the war ships and transports like I usually do and eliminate that last couple of AI's.

For me, the way to make the endgame less tedious is for the game to end sooner when it is clear that I've won. Of course, I could opt to not finish won games and sometimes I do that, but the isn't really fun.

Edit: as we all know, this is a problem in most 4x games. How do I win the venerable game of MOO2 when I am dominant? 1) I can build up a huge fleet and go to Antares and defeat it and win. 2) Most often I am winning by winning the Galactic Counsel vote with 2/3 of the vote. As I am often repulsive or won't be loved as I've conquered more than half the galaxy, I have to be large enough to be able to have more than 2/3 of the vote myself. 3) I can take the slower route and kill everyone.

Unless you make an unbeatable game theirs going to come to a point where there is only mopup. You could extend it where you require a really long game to beat. That is probably why they have cheasy surrenders. What you could do is use the computers decision making skills, and logical algorithms to make a more flexible gameplay, but there will come a time where you won. At that point it is mop up. Are you asking for an unbeatable game. I guess I'm asking for clarification on what you are asking for.