Yeah and air gives you the airqueens .
Both magic schools have though the problem that they don't work against SCs and probably later in the game the mages will be equipped with an air/fire resistence item too .
Especially the bloodnations have an edge here in midgame . If they face Airnations they can use a few storm demons and if they face Firenations they can use devils .
My problem is that i still haven't enough practical experience
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But i think killing SCs supported with some troops is almost impossible via battlemagic . If they are alone charm/soul slay etc. should work but if they have a bit support i think it is a real problem .