Why do we assume that "Nomura's original vision" was worth a damn? His KH plots are borderline incoherent (serviceable enough for what they are.. but no storytelling art), and he clearly wasn't able to corral this into a game. The world has sure given that man a LOT of creative reverence all because he can draw pretty well.
Give me a producer who can deliver a final product. The whole concept of an auteur's "original vision" has proven to be pretentious nonsense throughout this and many other creative industries.
As someone involved in the creative design process myself, the idea I once had of magic men passing down their perfect visions from on high is largely an invention of fans who really don't know how these things come together.
I can't speak for the others, but the reason I give a damn about Nomura's original vision is because it seemed interesting and ambitious on paper, while Tabata...really doesn't have much of a cohesive artistic vision of his own from what I've been able to gather from this whole XV drama. He just seems like the kind of guy who follows instructions and tries to please everybody based on feedback, and while that's not an inherently bad thing he just doesn't give me the same confidence as, say, Hiroyuki Ito or Matsuno. And like I said, Crisis Core and Type-0 gave me no reason at all to believe in him as a director, and while I'm not terribly fond of KH, they're at least better games than the aforementioned works.