You guys gave completely awful and facepalming answers about Kadir/Cadia. Resident Evil nurse? Dude get ur eyes checked, she looks nothing like that (she actually has a good character design). Nothing much? Seem like you didn't give her a fair look at what she can do.
Having the ability to buff elemental resistance and heal (from her 3rd class) has its uses as a good candidate for anybody's team.
Cadia was cursed with being a Main Job Cleric which means her base skills are very underwhelming as well as using maces and while she can white mage she doesn't get most of the really good spells a dedicated healer needs. She can Spell Blade but has low health which makes her a bad tank.