Which Final Fantasy are you looking for? If it's any of the older ones, you might have missed some of the golden oldies that are epic length. FFVII is the easiest example of this, since you haven't named Twig Collins, Miko no Da, or Knowing Shadows, all of whom wrote massive epics that are generally well regarded and contain few OCs at all, to say nothing of OCs with substantive parts. (I'll grant you that Twig's Long Hard Road had a couple, but they didn't become important until later and didn't ever feel like a self-insert, to me anyway...)