A few extra thoughts and suggestions that don't fit in the pinned topics.

1. City absorption cost.

It appears that currently, the influence cost to absorb a city by another city is proportional to the number of districts those two cities have together.

I think the formula is faulty.

In real life, when things absorb other things, it's easy to do so when one thing is big, and the other small.

The game, on the other hand, penalizes the player for having a big city, when the player desires to absorb another city by that big city.

Let's look at three situations in which city merging occurs.

City A is big, city B is big.

Currently: influence cost is very big.

How it should be: very big. It's hard to merge to gigantic cities. Here the formula works fine.

City A is small, city B is small.

Currently: influence cost is very small.

How it should be: small. Small cities are little more than outposts, and it's cheap to attach an outpost to a city in Humankind. The formula works fine as well.

City A is big, city B is small.

Currently: influence cost is very big.

How it should be: small. I think it's similar to a situation in which a central city in a metropolitan area expands its border and absorbs a suburb. The areas were already a part of one integrated city, the border change is a technicality.

Furthermore, if city B is small, it's little more than an outpost, and in the game it's cheap to attach outposts, but once B gains a city status, the cost for attachment becomes prohibitively high.

I would suggest to base the absorption cost only on the size of the smaller city instead, and in addition to increase it somewhat if two cities are similar in size (it's harder to centralize an amalgamation of two previously similar territories).

2. Revolutions

If I'm not mistaken, I noticed at certain points how areas previously belonging to an AI empire were now independent cultures, which could be influenced and annexed.

Was that due to revolts occurring in that empire, because of low stability?
I think it is a fun mechanic, how empires can fall and break up, but possibly, restore their power, and if they don't, other empires can compete for the newly independent territories.

Sadly, such problems with stability never happened in my empire, I hope they will be a challenge to human players as well.

3. AI quality

I gave some thought to what would constitute a fun Humankind game for me, overall, and came to a conclusion that balance is not the most important thing, as long as the AI knows how to play and is able to provide a challenge throughout the game, from the first era to the last.

I love the art and the music in the game, but they are only a part of it. Bugs can be fixed at some point. But the AI is something that will make it or break it, ultimately make the game fun.

From what I've seen, combat AI works more or less fine, but the empire management AI was completely inadequate...

AIs were lagging behind on era stars. That's the most important thing. 

All cities were 1 population because of unit spam, AIs quickly became behind on technology, FIMS were low, AIs couldn't deal with aforementioned revolts.

Please, do whatever you can to make the AI good.