This post just gave me an idea.

If Black Mage upgrades to magus, make it so that it gives you a slight buff to all stats and one, yes one, move that would bring the job to unrivaled heights. Something really OP that can't be used in PvP and has a long cool-down its so awesome.

For this to work it would have to be implemented during the later bits of the games life when the level cap is close to the max though.

Ideas like this are fun to imagine.