Not possessing the type of mind to adequately create the art that so much intense effort and money went into ... well, there's no excuse for that on an artistic or business level.
If he didn’t “possess the mind” they why are people still talking about SW 30 years later? Was ANH a fluke? Did he get lucky?
He didn’t possess the mind to create the art that you wanted to see. That’s it. Disagree with his choices all you want, but he made the movie he wanted to make. Some folks didn’t like it, some did. But you not liking the SE or the prequels doesn’t make the artist inadequate.
Casino wasn’t as good as Goodfellas. Is Scorsese an inadequate artist? I wanted Casino to be as good as Goodfellas and it wasn’t, should I hold him in “complete contempt” because of his inability to entertain me as much as he did before? Did Orson Welles ever top Citizen Kane? Did Ridley Scott top Alien? Are they inadequate too?
And on a business level… I’d say the SE and the Prequels worked out just fine… the hundreds of millions of dollars they made seem to contradict your poor LFL business analysis.