Ment
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Chaos isn't needed for survival, but to kill. The point is that while you're setting all this up, the attacker might manage to destroy a large part of the army (each cast takes 100% of the turn, not 50%), so physically, even such powerful casts might not be enough to kill the remaining units. But to last longer while the hero uses chaos/summoning – maybe.
I don't know. Maybe you're right. But I'm still skeptical. I'd like to see such a build in action.