Now we’ll never get the canon story of how Luke ended up after ROTJ.
Its like Bond just getting his license to kill and then we never get to see anymore movies.
That’s just patently false. We’ve had two different continuities exploring what happens after, and just because it wasn’t written by the original author doesn’t mean it’s not canon. Besides, Lucas never even wrote TESB or RotJ.
Lucas wrote all six movies he was involved in.
Leigh Brackett, Lawrence Kasdan, and Michael Arndt would probably disagree with you.
Leigh Brackett is given screenwriting credit out of respect from George because she passed away during early stages of the process of creating the film. It was also mostly already written before Lawerence Kasdan came into the picture. Little known facts are the relationship between Han and Leia wasn’t how he envisioned it and that he’s also said he had a big role on the film but his writing contributions were small. Funny how that works when many consider it to be his biggest contribution. That’s not to downgrade his contributions as he was definitely a piece to the puzzle like touching up Yoda’s dialogue but it’s overblown just how much he worked on it. George also doesn’t like taking too many credits for his own work according to Howard Kazanjian. He wasn’t involved in Episode VII. So you can scratch off Michael Arndt from the list of those you included.