Funnily enough even though I think the sequels have worldbuilding about on par with the original trilogy (why is there an Empire, what does it do, why are these people fighting it and why does Luke go from wanting to join it to being a rebel - we just don't know), I agree with your commentary about how this kind of stuff is really bewildering to absorb in the sequels. It's one of my major issues with the sequels and I do think it's unfair to expect fans to consume secondary media to "understand" what's happening on their screens. A good story should be able to convey this within the bounds of it's own narrative at least.

One of the big issues for me with the sequels is that I just don't get Rey. Like, I don't understand why she's joined the rebels. With Luke, you could understand okay he's drifted because of Obi-Wan's influence, but Rey is the one who wants to go all the way to the Resistance and seems to look up to them - and there doesn't seem to be any reason why. It's just this kind of disjointed thread between her wanting her family and joining the Resistance and it makes her very difficult to pin down in terms of motivation and interiority. And she's the main lead! You can't have your main lead feel this murky and unclear!

Tl;dr I wish the sequels hadn't hewed so close to the OT nostalgia thing because I feel in some sense it built in weaknesses which worked ok for the OT as a starting point, but don't work for sequels at all.