Should Lawrence Kasdan have been brought in to help polish "Rise of Skywalker?"

[ChrisIII]

Kasdan co-wrote ESB, ROTJ, TFA and SOLO along with his son so he's written a sizeable chunk of the 11 theatrical films. Granted/however, I think part of the reason he was brought into TFA and SOLO is probably because they were fairly Han-centric movies-and of course, ESB is perhaps Han's main showcase, showing some character growth as well as Han's instincts helping to keep the Falcon hidden from the Imperial fleet (Apart from the hyperdrive issue). It also doesn't hurt that he co-created Indiana Jones (Which I think got him the Star Wars gig in the first place, although EMPIRE came out first), although apart from a few surface similarities Han and Indy are quite different. (Indy for instance is a terrible pilot).

[Revolutionary_Jack]

Granted/however, I think part of the reason he was brought into TFA and SOLO is probably because they were fairly Han-centric movies

Bingo.

It also doesn't hurt that he co-created Indiana Jones

Lawrence Kasdan had absolutely no involvement in the creation of Indiana Jones or any character in Star Wars. The characters, casting, design, and concept was all done before he typed a single key, as was the major direction of those arcs. Indiana Jones as a character was developed by Lucas and Spielberg, and the concept of the Ark of the Covenant was developed by Philip Kaufman who worked with Lucas even before Spielberg signed on.

Lawrence Kasdan is primarily an independent film-maker who directs movies for adults, stuff like Body Heat, and the Big Chill. He's not at heart a genre guy. The work he did with Lucas on Star Wars and Indiana Jones were paychecks for him. That's all. He largely worked as a screenwriter and script doctor on ESB, ROTJ. He had no involvement in character creation, whether it be Yoda or Lando (introduced in ESB), Vader's plot twist, or even the Han/Leia romance. Lucas was the one who decided the plot, story turns, and character arcs. Kasdan could work within that fence but he never once tried to change stuff.

People need to stop building personality cults out of people who only played one part out of many in the production and development of Star Wars.

Ultimately if you have issues with Star Wars, then the problems are with you, not with anyone else who would have done better and fixed stuff and so on.