Ethics Divergence as it is right now won't even exist in Banks. Yes, there will be more powerful factions, but you can also do mroe to adjust your government to them and not all factions will have negative effects.
Exactly. There's no point to complain about ethic divergence in the current version. Even if you're right - and the fact that the devs are changing the mechanics prove it, so it's even more pointless to disagree with you, by the way. Currently, playing a fanatic individualist empire with no protection against ethic divergence is really annoying. You need to keep armies on some planets and to spend influence to keep them quiet. And it's not fun, because it just leads to angry rebels, not to diverse empires like it should.
But if you're still looking for a way to counter ethic divergence, try this if you haven't already:
- try to have as much influence as possible (protectorates are useful), so you can use it for the most problematic factions.
- unlock policies that please your people
- research buildings that increase happiness and ethic convergence
- don't grow too fast, try to vassalize other empires, or maybe purge them if they're too big (but I wouldn't advise it, the diplomatic penalty will be to big and you'd gain nothing).
You're also not supposed to play as a big hegemonic empire with those ethics, but rather as a powerful but little empire with slave planets (populated by alien slaves) and vassals. The good thing about angry slaves is that they are all gathered into the same faction, as opposed to free citizens who get one faction per planet (or more). If you don't want alien slaves, purge them, but you should probably build robots if you want to expand.