Well, Quina can be very useful, actually. Spells like white wind, mighty guard, etc. are really good, and Quina also provided the only spells that could inflict Freeze and Burn status. Not really useless.

I'd also like to mention something because I'm an obsessive compulsive freak... FFIX did NOT have a medieval setting. If anything it was more rennainsance influenced. I know, it's not a big deal or anything, I just go crazy when I see that.