Again, one of Rian's strongest points actually was Luke.
While he did butcher the character, in many ways Star Wars needed Luke throwing the lightsaber off a cliff. It's a meaningless device. It's a sword, yet people treat it like some statue that needs protection from ISIS. Luke threw away his lightsaber in RotJ because he sees where his future is with violence, and he throws it away in TLJ because he sees this woman where he was decades before and is trying to prevent it happening again. It's not good to have contempt for your audience, but I'm honestly so happy that TLJ was made the way it was. I found the film hilarious, and people too obsessed with seeing shiny swords from a fifty year old IP get slapped into reality.
Yes, JJ completely ignored TLJ for RoS. No, that's not a slight against JJ (or Rian for that matter). At the close of 2017 when Disney saw the reaction to TLJ, they still had $X thrown into the movies that needed to be recuperated, they just fired their director for episode IX because his scripts were (allegedly) terrible and were handed in late, they pushed the release back six months, etc. JJ was brought on the safe bet, because TFA was liked enough and he had major sci-fi experience at that point, having directed a previous film in the trilogy being a bonus. Unlike TLJ which was written and well into pre-production by the time TFA was filming, RoS didn't even have a proper script until after the first few months of TLJ's theatre run. Disney execs themselves, especially Kathleen Kennedy, actually got heavily involved in the writing for RoS, moreso than they had in any other Star Wars production to that point, and were actively telling the writers that XYZ had to happen at ABC moments.
You have to understand the context. JJ when writing RoS had to bring back fans who felt utterly betrayed by TLJ, had to fulfill the demands of Kennedy and the Disney suits, had to pick up the very few remaining pieces left over from TLJ, had several less months to shoot and edit the film, etc. The film released in December 2019, they were still doing reshoots in October/November. By contrast, TLJ wrapped principal shoots in February 2016, giving them almost two years until release to work on reshoots, rewrites, edits, etc. There is only so much one man can do, only so much blame can be levied on his shoulders. Personally, I put none. There were zero realities where RoS was going to be a good film just based off the burnt threads at the end of TLJ alone. Add in the extreme crunch on filming and writing RoS, not even Spielberg could save that disaster ticking away. Palpatines, Skywalkers, it doesn't matter because no one cared after TLJ. If you said Rey was a Windu people would have been fine with it because people fucking hated TLJ and were simply happy to have that film rebuked "officially".
I don't think Zori Blis did anything to hurt the films. These characters are there for twenty seconds, they take a day of organising to write, cast, book and shoot, it's a way for JJ to get money from the back end and keep washed up friends happy, nothing more or less.