To the thrust of the main question - I am one of the lucky folks without major performance issues, and the verdict is, the game is quite playable, if you use Glavius’ AI and also set the difficulty to max (Scaling or not, to preference), and if you disable the crises.
The AI in the game as released is currently not able to actually play the game with the new rules they have instituted- I don’t mean that they are strategically inferior, as has always been the case (and is understandable), I mean the AI literally doesn’t know how to use the new planetary rules from this expansion, can’t upgrade or repair buildings, and thus cannot build fleets or really do much of anything else.
Glavius’ mod built in some events to force the AI to upgrade buildings at the appropriate time, and disabled the functionality of buildings being ruined by war so you don’t want up with every AI planet full of permanent wrecked buildings. Throw in Grand Admiral level resource bonuses, and you get something like a functioning galaxy, which lets you actually enjoy the legitimately quite interesting new features.
The crisis is currently just broken - they literally left the code unfinished when they released it. Fortunately, you can turn them off. (And Glavius is actually working on a fix for those, too.)
So - with mods to patch some of the more gaping holes, yes, playable. Without, no.