I totally get dropping the number naming. Heck, bands have self-titled albums well into their career, and movie franchises do it, why not games? Especially if all of the entries don't tell a linear connected narrative.
(I mean, having played only 2 non-consecutive Final Fantasy games, I think the way they work is to re-use some themes and concepts but each game is its own completely different story, right?)
I remember seeing an observation that the only two genres of movies for which having sequel numbers after, say, 2, are horror and pornography- that is, genres that are not respected in the mainstream. Godfather 3 was kind of a big deal calling itself that, and then the movie was not good anyway. "Prestige" films don't have a number after it.
So with the producers of Final Fantasy being very blunt about how they want to be considered part of the cinematic prestige game world like God of War and Last of Us, and how much they care about story, I'm actually surprised they kept the "16."