More than anything else, what upset me was the lack of planning. Disney was handed a respected IP and they betrayed the three primary characters (and their actors). And someone, somewhere should have recognized that based on life history, the first movie should have been Carrie Fisher's.
There has certainly been mismanagement of the property.
I don't know if Kennedy will be gone as you say. She has said she isn't going anywhere. One can hope. But I do find it interesting in a car crash sort of way that the same group that can give us the garbage of the three sequels also put out Rogue One and Andor. It shows they are capable anyway.
She says she will hand over the reins, but remain as a producer on the projects that she's involved with.
As I've posed before, it would have been interesting if someone like Kevin Feige, who resurrected the Marvel franchise for Disney, had been given the reins instead. Of course, he's also shown that the success rate is not 100%, and external factors have also weighed on the property of late, including audience fatigue.
No doubt it is a difficult job, that requires being adept at balancing the creative aspects and the business aspects.
Favreau and Filoni are naturally mentioned as possible successors, one or both, but there are doubts whether they'd want to deal with the business side, which is a greater part of the job.
I think however, that a writer being protective might also have something to do with it. Gilroy knew that if HE did not write Kleya and Luthen's backstory, then somewhere, sometime, someone else WOULD. And it would be canon and out of his control. So, he wrote it. And now it's canon and no one can change it.
It's obvious that no one writing the sequels cared that way.
Not being an insider, or a character familiar to the franchise or genre (though he was part of the Bourne franchise) worked in his favor. As well as a lot of the actors, who didn't come in with, or feel the burden, weight, or whatever baggage comes with entering, and becoming part of the SW universe.
For them, they wanted to tell a good story, and had no qualms about declining to participate if they didn't feel the quality was up to snuff.
That also applied to the other principals, like the directors and other writers. Some of the best dialogue in the series (including Luthen's first encounter with Lonnie) was written by Beau Willimon, whose creative CV reflects that, and also worked professionally as a political speechwriter.
It sounds simple, and stupid to repeat, but hiring the right people, and allowing them to do what they do, helps tremendously with the chances of success.