Sounds like unnecessary complication. They could take it back to old school (well, at least FF5).
Can use lower level Magic skills as to not impede on healers and magic dps.
But power comes from quick casting (which can be proc based via melee attacks) and double casting (which can be consumable buff based like aether). So it may not be uber burst, but has fast steady magic + melee dps.

Wouldnt want it to be a debuffer as they have a multitude of other jobs in FFDom that can fulfill that role to a better ability.


Another option would be that it could take the Mystic Knight role. Enchanting its weaponry with elements that yield different effects per strike.
Fire burn, Ice slow, Lightning stun, etc. and could have combination element attacks that deals a combo attack (think Riftblades in Rift, just not as stupidly OP)