I completely agree with you, most of the time I have to turn the option off or avoid it like the plague. Sometimes, just by building a strong economic backbone, I would assimilate most of my neighbors without a single Influence Starbase in sight. The recent changes have made the rebellions even faster, so the other side never has a chance. I have to intentionally ignore the culture tree just to slow down this effect (perhaps making these tech a lot more expensive would balance it a bit).
Personally, what I find most disturbing, is that while the Altarians try really hard to push culture (all those influence starbases when they have spare constructors), they NEVER build any farms to raise their based population influence (which also makes them the WORSE trading partner ever). Meanwhile, the Drengins will build so many farms that they will never ever have enough morale to reach the limit off (they will have enough farms for 28B+, but their morale is less than 40% at ~15B, so they never grow anyways). Couldn't we, like, get the Dregins to split the amount of farms that they build and give half of that to the Altarians? so that they are both more effective at what they do? (Observed mostly from 1.0x, since these two guys just haven't been living long enough in my recent beta games - so I appologize if it was already adressed).
But to answer your question, why did Culture Domination get easier? Apparently, the reason it was so that people could "clean up" games that they have already won with less effort. Essentially, when you've pretty much already won (control half of the galaxy, and the 3 times the size of the next guy) it's useful so that you don't have to go world by world and conquer them (which is a hassle). Just build some starbases and click "end turn" a bunch of times and voila. This is done mainly for Metaverse people I think, but since I don't really bother with it anyways, I just turn the option off and quit if I feel it's getting boring.
PS: If a dev is reading, is there any chance you guys can make some of these culture conquest values/conditions modable? I know I can lower influnce from tech, but that hasn't really helped that much (I avoid the whole tree and still dominate people). What I mean is amount of influence population generates, the amount limit that it has to be before revolt (IE: something more than 4.00), and the chances that a world would revolt if it meets the condition, etc...