Good article about the issues with the creative process that got us here.
“Conspiracy theories abound regarding this film, but the truth is probably dumber and more well-meaning than angry fans love to hate to believe.”
https://birthmoviesdeath.com/2019/12/31/decoding-the-rise-of-skywalkers-difficult-creative-process
It’s a good article that tries to look at what went wrong rationally, and I agree with many of the conclusions. But I think I probably fundamentally disagree with the idea that reverse engineering a story will always end in disaster. Maybe here it did, but when it comes to endings, I think it can be very important to work backwards. Some of the things they did - like mapping out unresolved questions from the previous films - you can easily see scenarios in which these things end up working.
Ultimately I think the basic fact of the matter is that they started from a place where they were trying to accomplish too much within one movie and they didn’t have enough time to whittle it down to a more manageable length. I fully believe most of the post production changes were things that were done to simplify the narrative (that ironically might have complicated it in other ways).