[Squirrelloid]

That crumble is bugged is well known. But you're wrong as to how its bugged - it totally destroys any wall its cast on, not merely 150 damage.

Of course, then attacker/defender effects are applied afterwards, which is why you feel like you didn't make progress, because as the attacker you can't see the actual state of the walls, and the defender is repairing them faster than you can destroy them. (Crumble's effect happens during the magic phase, armies repair and destroy sometime towards the end of the turn).

Crumble is supposed to make sieges go faster, not help you siege walls you can't otherwise break.