Versus XIII was announced in 2006. XIV was announced in 2010. FFXV was a problem before XIV even stepped on the scene.
I understand you feel for Nomura, but just as you suggest some posters are being cold with regards to his departure, I feel like some of your posts undermine the importance of accountability.
Nomura is (was) director, so yes, the blame is coming down on him. That's kind of how it works, in any industry, on any project.
Before XIV was a problem, XIII was the problem. They had HUGE production problems before versusXIII was even off the ground. Really nothing was being done on versus. XIII was actually planned as a ps2 game because they weren't ready for ps3 architecture. Then during XIII pre-prod they switched gears to put it on the PS3. Now for must of it's production it was in mind to be on the PS3 because that decision came early on. But Square wasn't ready, the PS3 was giving TONS of developers issue right at the start of that generation. They weren't prepared for the expenditures that were required.
As the project balloned the lost creative vision, and the dev team had all these siloed verticle slice concepts that couldn't be integrated into one vision of the game. Tones of effort was wasted, tons work was scrapped.
Once they spent so much effort, they needed to push out sequels which would have a low development cost and turn around after spending so much time and money laying the ground work. They also doubled down on the fans that they knew they could count on.
versusXIII/XV had way more issues related to squares problems as a whole than any problems distinct to that team. The issues kept plague them, and they were the project that was pushed to the back burner time and time again. Kind of like the class that you ignore a bit when your about to fail another.