FFXII, XIII & XIV suffered from SQEX failing to adapt to more modern development practices (though certainly there were other missteps taken as well) which made their game development inefficient & hard to manage. FFXV was mostly a victim of the prolonged development & the aftermath of the release of XIII & XIV. A "Versus Saga" probably seemed like a good idea before the FF franchise had been dragged through the mud for almost a decade, less so after its full production was delayed until PS4 & X1 were almost upon us and after XIV 1.0 and Toriyama happened.
They've been working on improving on their weaknesses ever since the double-whammy catastrophes of FFXIII & XIV1.0 and they've been showing some obvious signs of improvement, considering they are actually able to actively develop games like FFXV, KHIII, FFVIIR, DQXI, Nier 2, World of FF etc. simultaneously instead of a single game hogging their development pipelines completely, like FFXIV ARR did. The only way I could see them failing to improve further is if they release a commercial flop after commercial flop (as far as JRPGs go) and that discouraging them from even trying anymore. Not that I expect them to release FFXVI in 2018 or anything. Developing modern AAA(A) level games with the scope & ambitiousness of FFXV takes time no matter how good your development pipelines are.
None or very little of it is Nomura's fault, that's silly to even theorize. While he has been more than "just" a character designer for the franchise for a long time, other people have still far outranked him and made the final decisions when it comes to the development & direction any particular FF would take. FFVsXIII was to be the first mainline level FF Nomura would actually direct & be fully responsible of, so blaming him for XIII & XIV is silly as hell.
You were doing so well until you went off on a subjective rant. FF XIII was not a castrophe and while not the critical darling 12 was, the game received largely positive scores ( see Metacritic). The creation of XIII-2 and LR were due to the FFXIV reboot eating all of SE's resources and the ability to use deleted and recycled material to create full length sequels. It's okay to not like XIII but SE counts the entire trilogy as a success.