if you were level 70, youd be able to heal 40k-50k hp every 2.5 seconds, now, i dont know what type of output healers per second are supposed to have, but i feel like a tank should have a hard time dying with 2x that heal amount. yeah, there are mp considerations, but even with 5 seconds per heal that would be massive.
regardless, my point is not that blue mage are better healers overall than healers, merely that they go way beyond dps regular limitations in healing and tanking. Its not questionable that they can do it outside of savage, which is where the vast majority of players play/use DF