A Warrior hero from the Dungeon faction? That's absurd...

Jalib is generally an underdog among mages; ignoring his specialty isn't a problem: mass spells aren't reflected, and area-of-effect spells aren't reflected.

Why summon creatures against a mage – that's a big question, especially when there's overwhelming chaos magic that ignores all magic defense. In later battles, the Tribes of the East will likely lose to a mage, but if we're talking about early attacks, not everyone can compare to them.