Bottom line, I have yet to play a game in which i was limited by population in any way past the first 10 turns. Given the current mechanics of the game its pretty easy to reason out why this occurs.
Beginning game. Current base hub production for population is 1. First structure you build is beacon of hope which takes 3 turns.
Turn Population Growth Rate Event
1 0 1 Start building beacon
2 1 1 Start building farm
3 2 1
4 3 2 Beacon complete
5 6 2
6 8 2 Farm complete
This is the only opening strategy that makes sense on turn 1-6. All other structures are unavailable until turn 5 due to population limits.
Turn 6 things get interesting (but not that interesting), do I build a lab, hut, workshop, or study? Now that we have 5 materials this actually becomes a choice, your next decision point will come in 5 more turns. If you build a hut now you'll be up to 18 population, but you'll have zero materials. And then must wait another 8 turns (workshop build + material production time) before you can build something else. If you build a workshop now you'll only have 10 pop, but will still have 3 materials. Lets say we build the workshop, because this actually make population closer to being a constraint.
turn Unused-Pop Growth Rate Event
11 5 2 (constrained) Workshop complete, Start Hut
12 5
13 5
14 5
15 5
16 7 2 Hut complete (now you can grow up till 35 unconstrained)
Now I usually start building arcane labs or studies, depending on what heroes I've recruited. First one costs 5 pop, you have 7, no problem. After that it just gets more imbalanced. (if you built the hut first its even worse for population as a resource).
From here on out population is never a concern (it didn't even play that much of a roll in this calculation). You have a growth rate of 2 per turn. All the buildings you have a construction time of 5 turns. They all use 5 population. Thus you're gaining population at a faster rate than you can construct buildings that use the resource. Suppose you also want to constantly train peasants (units with the shortest construction time) as well. That just takes another 1 pop/3 seasons. Total population use per turn = 1.33. Still well under your growth rate. Throw in the fact that you're also constructing buildings that don't require any population (inn, huts, etc.) and you see that as currently implemented your population will never be a concern again. Gets even worse when you start factoring in palaces, inns, etc that increase your growth rate even further.
Other cities start with .7 growth, but throw in an inn, or a hero with a little charisma and this also climes above your construction rate in the city of 1pop/turn (if you're training a unit its 1.2 per turn in most early game cases, unit takes 5 turns costs 1 pop).
The first resource that constrains any of these calculations is food shortages (which is how its supposed to work). With only your capital's fertile land you can't grow past 135. Given the rate of growth above you reach this at around turn 80-90 (if you've been building huts at the proper times). During this time you could have constructed buildings that use at most 65 population. Thus you still have 70 unused population in your capital alone at this time, or an additional 60 turns of production (at the building plus unit rate) taking you to turn 140-150 with no population constraint. This is assuming that you didn't find any other food resources nearby, didn't research any food techs/housing techs, didn't invest in green thumb, didn't find any farmer heroes, etc. The chance that none of these things have happened is near zero, so we can assume that your capital, and any outlying cities continue to grow. In most of my games this is the case. I'm almost always able to keep my pops growing.
Because of all of this I NEVER have to even think about population as a resource, just keep my pop growing in order to build my tax base (Gildar actually does constrain me sometimes). Pop as a resource is meaningless as of the current build.
Suggestions-
1) Increase the population cost of all buildings or reduce the growth rate. Essentially, you have to make the pop/turn production rate of any given city > the population growth at any point in time in order for population to ever be a constraint on production. That is not the case currently.
3) Make units cost more population from the very beginning. For instance have the base unit be a squad- 5 soldiers, next platoon- 15 soldiers, next company- 45 etc. When even the most basic unit cost 5 population it starts to become a constraining value. Once again this just boils down to adjusting the pop/turn production rate, but this has the added bonus of really forcing a trade off between military and production, a trade off that is entirely lacking now.
2) Keep the current population numbers, but make population valuable for some other reason than just as staff for our buildings, soldiers, and taxes- here's one suggestion that I had https://forums.elementalgame.com/401657, maybe change it so only unused pop in a city contributes to additional production. Keeps the focus of elemental on the scarce population and food in the world, but obviously a more major change thats would be implemented until an expansion.