I find that Proteus is much more useful because of all the rare mana blessings. I’ve combined him with cChao which works pretty well as cChao will absorb all the mana on the second turn, so after Proteus’ mana block wears off, you get cChao’s mana full. As a result, that targeted boss never gains mana for 2 turns even when hitting with lots of tiles. With the two of them, I can pretty much keep mana generation to a minimum. I’m on level 25 of impossible and find that I can usually fire them off every 2-3 turns.
I guess one of the positives are the blessings that allow me to fire specials all the time. In addition to the healing blessing for health with specials.