As much as J.J's given shit here, I think the original framework laid down in TFA could have worked:
- Although vague, Snoke was an interesting villain that certainly had potential. Where did he come from? What history was between him and Luke? Why did Kylo turn? He very well could have been built into a character that carried the trilogy.
- Rey would have been better received if her and the whole crew (sans Solo) had been saved by Luke at the end of TFA, as she wouldn't have been powerful enough to defeat Kylo from the very first movie. Even so, she was still salvageable through humbling in the sequel via the original ending. That part could be considered an Empire retread, but fuck me I wouldn't loathe her as much as I do now.
- Finn with a more significant role could have helped this trilogy a great deal. Delving into the perspective of these new stormtroopers of the First Order, their abduction and mental conditioning; something to complement all the Jedi hubbub in-between. Maybe an overarching narrative in which they serve a more important role. Hell, if this new trilogy had fucked off with "The Force is Female", focused on "The Force is With Us" ("us" being a catch-all term for "everyone"), and kept holding Rey and Finn as dual protagonists throughout, this would have gone down a lot more smoothly regardless of sex or ethnicity. And that's without saying anything about Poe.
- Captain Phasma was still alive by the end of TFA and could have been built up much further in the sequel, dealing with her own defeat to Finn and being at the forefront of the First Order's offensive. Her presence really would have made more of a difference to Finn's story, and could have obviously overlapped into Rey and the others had she been given a chance to do well, anything.
- Likewise, Hux serving as a dual antagonist with Kylo would have helped. Turning him into a joke made the First Order into one by extension. I'm sure to nu-Wars fans, they still looked threatening, but to anyone else the menacing nature was gone.
- Rose didn't exist. 'Nuff said.
Rian (and to an extent KK) squashed any chance of IX being potentially good shy of discrediting VIII as a Force fever dream, but Disney would never do anything like that as they'd have to admit they fucked up. Make no mistake, if VIII hadn't been touched by Rian the trilogy probably still wouldn't be anywhere near as good as the OT, but it could at least have been satisfying. It could even have been rearranged and still involved the deaths of Luke and Leia somewhere, the potential was indeed there to wrap it all up. But TLJ fucked all that up and closed off every possible avenue that didn't require an immediate retcon and ensured that characters both old and new were utterly humiliated before dying or being written into a corner with no escape.
In short, J.J's worst contribution besides the retread was giving too much agency to Rey in TFA. Rian's worst contribution was running everything into the shitter while telling us how special he considers himself to be.