We know enough to say that Tabata's version of the game is way different from what Nomura had originally planned. Stella, who was an equal to Noctis and had the same powers as him, got replaced by Luna, who was poorly developed and died so quickly that you had no time to develop an emotional attachment to her. The Emperor of Niflheim and Verstael, the Chief Scientist of Niflheim, were originally intended to be main villains in Nomura's version, but in Tabata's version they barely show up and both die off camera. Ignis was supposed to be Noctis' military strategist in Nomura's version, but ended up basically being Noctis' butler in Tabata's version, English accent and all. The planned Insmonia invasion and subsequent escape from Insomnia by Noctis and his friends was dropped from the game entirely in favor of Noctis and his friend's already be gone on a roadtrip when the invasion happened. We know other details from a leak, but I won't get into those here since they aren't confirmed. We also have a good idea for what Nomura had planned for the combat system, based on what we've seen of Kingdom Hearts 3, which is way different from the hold button to attack system that Tabata came up with. In my opinion at least, Tabata did botch the game, though I don't think he is entirely to blame, it is clear that Square rushed him because they got sick of waiting for the game, he basically rebuilt the game from the ground up in 3 years.
That's not really him botching the project though he likely had to rebuild the whole project because the was little actually developed to make a game with much like with VIIR where the trailers where nothing more than tech demos and not actual games and with the management wanting the game out had to make cuts. Combat is the only real thing I agree with here the KH style approach should have been kept.
The real problem is that the project was hijacked to be turned into XV with the thinking they would get the next entry out quicker while being able to start KH3 but now they likely would have been better off just creating a new ground up project for XV and let Versus finally be developed.