I've noticed what I think are a few balance issues with endgame.

First is the stacking of tech cost reductions.

So far I'm aware of:

-10% from ITER

-20% from Genius of the Endless

-20% from Sophon final collection

-20% from Mezari final collection

AFAIK they stack additively. In any event the problem here is that there are way to much of it “in total”.

I stacked ITER + Mezari + GotE and the rest was the most disappointingly quick science victory I've ever had in any 4x game.

Reduce their number, and/or reduce their size, and/or make them stack multiplicatively. Or even better switch some of them to science output increases (if you ask me it's the collection bonuses that are the prime candidates for that).

Speaking of Mezari, IMHO neither one of the empire quest line alternatives can compare to theirs.

Not only is it the easiest one, it's also the most beneficial one. The “stay UE” is particularly pathetic (essentially you don't get ANYTHING from it), and trading +1 influence for a manpower bonus is not such a great option either.

Then there's trade.

First time I got decent trade going I had to join an alliance to stop trade from interfering with my victory type plan.

It's nearly impossible to have good trade going and NOT win an economy victory. Unless you specifically take steps to prevent that from happening.

If you ask me trade in general needs to be less extreme. It's completely worthless on a bad setup, and completely OP on a good setup. That time I used alliance to stop economic victory from happening I've had around 12k dust per turn (and needed around 250k more for a total of 450k to win) when I noticed that I had to do something about it, and at the latest point I remember I had around 24k per turn. Wasn't even a Lumeris game.

Alliance victory needs balance in general. For example science victory in alliance of two requires you to have 6 VTs between the 2 of you. Meaning that one of you gets 2, one gets a third and so long as you share them with each other through diplomacy you've got 6 in total. Or even if you can't communicate with your ally (for example on account of him being an AI) you can just get all 3 yourself and give them to him. It's still faster than doing all 4 alone.

Also, peaceful victory conditions seems too easy in general compared to militaristic ones.

All 3 of them are a LOT easier than supremacy (on anything but the smallest maps that is).

Conquest is on the other hand too troublesome. Primarily on account of over-expansion.

However, if you ask me it's the conquest that needs to have something done about it, not over-expansion.

In the first place expansion penalty system is crucial, and I believe that as far as wars aren't concerned it's looks well balanced. Can't say for sure, haven't tried all the maps&number configurations out there, but with the ones I played it looked great.

Which leads me to an idea of counting one's own systems and conquered systems separately. Though that may be problematic with some factions.

In any event I'd sooner not have conquest victory than have a game where it's ok to hold as many systems as conquest victory generally wants you to.

If you ask me a good limit is when you can cover ALMOST the whole map with combined limits of all the enabled players. And that's how it seems to be working so far to me.