Made another post to explain where my doubts lie.
I'll make an example too:
FF1: you chose a class and learn abilities from that class.
FFT: you chose a class and then chose abilities from other subclasses of your choice.
FF10/12: you have archetypes and then freely chose abilities from a skill-tree.
FF4: you have unique characters with special abilities each. No choice.
Edit: I ask that why?
Cause if we have pre-established heroes with unique characteristics(FF4, FF8, ecc), then designing a lot of classes is an unnecessary work, you can just design single characters and likely you'll see many classes disappear from your list.
While if heroes are up to customization, then there must be a list of skills to chose from, in which case you should limit what we're going to pick about these outside characters we're giving you.