I suppose it’s not that bad. May not be noticable in the late game but nerfs early game hard. They could’ve let all spell damage remain the same. It would even promote Oracle usage (and choosing between mass Oracles for attack vs just traps).
Also, to use it effectively, since they don’t stack, you’d need to have units affected by as many different spells as possible. So more upgrades to research and fewer units to have.
Makes her stronger vs ground (Corsair DW is not energy dependant) but that was never her problem anyway.
PS. Vora P2 discussions go here 
Surprised No Discussion on Vorazun P2 