I don’t really think TFA screwed over TLJ & TRoS that hard. Redoing the Rebels v Empire conflict was a mistake, but they could have brought in the Republic military as late as in Episode 9, and there’s more interesting subtext to the conflict you can read into TFA and TLJ.
They don’t develop on the new concepts of the ST that much, but TLJ picks up the slack enough that I don’t think it’s a problem. At least in TFA’s case.
The Knights of Ren should’ve been cut, because there’s not really anything you could do with them. That’s kind of indefensible, but it’s not that big a deal either.
I don’t really know what else could be a case of TFA screwing over the rest of the ST, though.
Rey’s identity shouldn’t have been a mystery, Poe should’ve died early on as planned (so that Finn could have his role instead of just being a jedi decoy for Rey), and if they were gonna put Luke on an island, then maybe don’t have him standing all elegantly with Jedi robes. I get that they wanted to take artistic license there for the sake of making the ending of TFA feel “hopeful,” but in-universe, it would’ve made more sense to just have him already in rags and maybe just sitting on a rock looking all sad or something. Make it clear right away to the audience that we’re getting a sad hermit Luke.
I’ve been meaning to say that last one. I agree completely with it. I think I agree with your other points too. I hadn’t really considered the Finn one in that scenario but I definitely do think he should’ve been given more to do as if anything we could’ve seen him and Poe clash heads about saving the stormtroopers and for them to join forces against a greater threat. The Knights of Ren perhaps? I think that would’ve been very interesting.
I do wonder if TFA would’ve helped bridge things better if it ended with the Falcon leaving D’Qar and we’d have no expectation of what Luke would look like. Our first true look at him would be in the rags and wondering why instead of the jarring shape shifting.