I think everyone is blaming the wrong people. The success and failures of this game are mostly a joint venture but if anyone caused the snowball it was Toriyama. Because he is one of the higher board members he got to make his game, FFXIII take precedent over Versus. Originally they were being made at the same time. FFXIII hit so much trouble that they started pulling Nomura's team onto it. One of the most damning things for Versus was when the already complicated process of making an engine had to turn to focus on a less complex game. Crystal tools should have been made primarily for Versus first, then XIII, that would have made the transistion simple. I swear I remember hearing that at one point Versus was ahead of XIII. Yet after FFXIII released they were left with the question on how to transition that same engine to work with a much broader game.
Nomura suffers from being too artistic and creative for his own good. I will say that. Much like Kojima..... he needs a handler to get him to scale back. I think even if the engine had not impeded him so much he might had over promised. It sucks because he kept having to be stolen away from his own projects to help with others. He is probably the most worked of all the Square Enix creators. Remember.... Square snuck in 2+ extra games into their timeline of the FF Versus XIII release. XIII-2 and Lightening Returns added to the derailment. I honestly think that once Nomura saw he was not going to be able to make the game that he promised, he no longer was up for it.
I distinctly remember leaks starting to happen the year before this console gen. They said that Square had planned to quietly scrap Versus after years of delays. Problem was....once that leak happened SquareEnix Stocks plummeted. They quickly put out a statement that the game was still in development. I think the game WAS actually cancelled, and everyone involved was ready to move on. Yet the Shareholders recognized FF Versus as the most appealing looking entity they had revealed and the hype for such a game would never just go away quietly. Many a share was bought on the premise of this game afterall. So at that time they kicked back into overdrive, but now they were given a time limit...... FF Versus XIII, now FFXV had to come out else so many deals were about to be broken.
This is where Tabata got tapped in. He was one of the only SE devs churning out his projects in a reasonable time, many of which were well received. He came in as the fixer for this game. Yet......I think some of his liberties ruined the spirit of what the game was promised to be, even with taking in consideration . Mainly....Luna. Why? One of the most appealing things of the original Versus concept was Stella, a badass Rapier wielding counterpart to Noctis. The removal of Magic was also damning and the limited level of control of the party members when they were previously stated to be uniquely playable was unfortunate.
Final Fantasy XV could have a movie written about it, it's development had so many turns.
Honestly this why I think some developers were better on limited hardware. In the case of Kojima, I enjoyed his older works far better than his new ones. All technology of the newer platforms is great, but for really creative types it seems causes their imaginations to run wild and not in a good way.