I expect five level spells to be very powerful. In the current mechanic there is no point for two heroes ever be in one army, due to really bad experience cut. Thus, in my games i either have mage, who does not need giant form, or i have a warrior who cannot cast it ....
My suggestion is:
please, allow giant form to be cast on regular troop, just put it on cooldown, so it is not abused.
