Poor management from the previous CEO is the main cause of so many Square games taking so long, particularly in the case of Versus XIII/XV.
Nomura's pretty efficient, all things considered. There were seven Kingdom Hearts games released in the first ten years of the series, all directed by him, plus two remakes. KH3's taking about five years, but that's hardly unheard of for massive games like that. Especially since partway through development they had to switch from Luminous to Unreal 4. It's surprising an engine change didn't set them back further, honestly.