I quit this game around a year or so ago, let me tell you, and I couldn't believe that there wasn't a huge outrage over the lag, or people kept playing the game without complaining about it, and then I noticed that most players don't even play on the fastest speed, which is why it took so long for the outrage to compile, if most players did play on fastest speed, they would have complained long ago, way before pops, a bit before and after wormhole stations were removed(the in between patches had fixed the lag for a while, and then it went fubar)
But I kept looking everywhere where is this magic potion that makes the game playable to all these players, the suggestions were awful, amputate your game so you can play it(specific settings, use mods, etc.) why bother? I might as well not play it, but even with trying those suggestions it never helped, it's like castrating yourself in ck2 because you got the flu.
It used to be able to be played till year 2900 fastest speed with lag of course but it was by far not THIS bad, it was amazingly fast early, good midgame, and tolerable late.
The one who posted the times per month, 8 sec for early game is HORRIBLE, even 4 secs would be terrible, early game should be lightning quick and that's how it was, go boot up a ck2 game and see how fast it goes, 2 years will pass before a min has passed.
And it's not just the population, the lag got worse with each dlc they added and this was before the pop overhaul that I quit, I tried it after and it was still the same.
Right from the get go the first 5 years are unbeareable, it lagged even more than when I did a slave conquest with the largest galaxy and habitable.
With every new dlc no matter how light it is, the lag gets exponentially worse.
I think there is NO FIX for this, which is why they don't talk about it, which is a huge shame because the game is amazing.