I like the tank idea, just nitpicking but mighty guard is in the game as tank limit break. And yeah the tanking thing could work with lancer, if the job crystal grants enmity to the full thrust combo, piercing talon, and doom spike. With my original idea I just don't like that it could make blue Mage potentially useless in certain fights, where mobs or bosses would either not have anything to teach or teach something useless. This would be very difficult to balance out and consider. Also, magic hammer in that case would deal low damage and return it as MP or TP and still have its stun/silence/paralyze function.