Heroes 5.5 WarGame Edition - Tactical Edition.

I think you've weakened Chaos magic too much. I understand that it was too strong at the early levels, but in large battles, it was weaker than other schools. Now, there's no point in taking it at all – the hero deals much more damage. Guild wizards specialize in combat magic, but their magic is weak (they shoot stronger), so it's more beneficial for me to take star mages, who shoot with direct targeting.
Chaos magic can be weakened, but not to this extent.