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

"A punishing strike helps a Knight a lot, but a Warlock very little."
Why?
The effect is just as good. It's devastating against Chaos, but if there's no Chaos, only the troops remain.

Because a Knight is "destined" to use Light magic! It's one of his primary focuses. Light magic is important for a Warlock, but mostly to reduce losses. In other cases, it's much more advantageous to spend the hero's turn to destroy, say, eight level 8 creatures with a single spell (of course, with the Lucky Charm skill).