Again, this is why Gary Kurtz was purged from Star Wars so that we can never have a perfect trilogy and have thirty-five years and counting of unrelenting misery.
According to the relevant information available, Kurtz was fired already during ESB because he didn’t manage to do his job as a producer. He let principal photography to go way over schedule and way over budget (something that is unacceptable for a big studio production, let alone self-financed production). Even if he stayed things wouldn’t be much different. Lucas always had it his way. Even in ANH since studio didn’t seem to care.
Convenient excuse; Lucas was jealous that Kurtz made a better film than he ever could. Empire is the best because Lucas has almost zero involvement, and conversely Jedi is the weakest. The Ewoks and twincest were all George’s idea.