I don't think Black Mage will ever stop being awesome unless it's blatantly nerfed. However, why not... *rummages through wiki pages*...AHA!
Sage. Sage is usually unique to specific characters, but appeared as a playable job in FFIII and TA/TA2. It's known for using the strongest spells in the game, but I think to balance this SE could incorporate them as slow but powerful casters. They could be given non-elemental nukes like Ultima and Scathe, for the players that want to see BIG BOOMS!
They could also go with Red Mage. Give it access to Conjury and Thaumaturgy, give it some sort of chainspell or multi-cast ability, and it doesn't necessarily need a sword. I mean, apparently Archer doesn't need to be Ranger, so all bets are off for weapon types.