As Sony said in relation of Call Of Duty:
FF is a 'genre' by itself.
I agree with this.
Squeenix's mistake, IMO, is not fully embracing this concept by creating some sort of cohesion within the brand.
This interview glosses over the fact that sandwiched between the releases of 15 and 16 they
re-released FF1-6 as pixel remasters to tell those stories again, and then released Stranger of Paradise which is
another take on the FF1 story, and then additionally are releasing FF7 remakes.
They have this universe that they love telling stories in, and you would think 35 years of fan goodwill would give them the confidence to tell stories in that universe that fans have some background knowledge of, to give us those "ah ha!" moments. Ala Disney with Star Wars.
I say that to say: give me a glossy, hardcover, 500 page atlas of the Final Fantasy universe. Connect the games, detail the summons, give me some chocobo evolutionary history. Make the call which things are canon, and which things aren't. Then, don't worry about mainline entries, just tell different stories in different areas of the universe that you want to.
Show me the Warriors of Darkness battling the flood of light in FF3.
Show me original 4 warriors who sealed ExDeath away.