Fair enough ! Though the Materia System and how you use it is basically up to you. Do you want Cloud as the healer? Done. Vincent as the Black Mage? Done. Tifa as the brawler with no materia expect for protecting materia ? done. Barret as the summoner? Done. Cid as the Blue Mage? Done.
Or you could just keep some things fair between the party and give everybody a bit of healing and elemental magic each, or just give everything to Cloud, or not really use materia for the party at all, or even just have the summons or protecting materia.
Yes, they can equip the same materia and be a mage, but only if you make it so.
You could " FF3/FF5 " everybody with a "job class system ", or you could do something like FF10 and have a "summoner ", or you could "FF8" things and a keep a limit on magic use, unless you have too.
I thought that you meant characterization wise though, which is why I was disagreeing so much because one character believes that he's somebody else for a decent chunk of the story, and another character is a talking dog.
To be frank though, all of the FF's can, if you allow it so.