How does this attack work out?

I'm too lazy to test it myself :D

it doesn't...

prot from magic weapons stops all magical weapons, and arrows of dispell are flagged as +1 arrows, magical...so pfmw will stop arrows of dispell

now the dispell casts as a 10th level mage, when you hit someone wearing stoneskin, its as if a 10 th level mage casts dispell or remove magic...however since a grandmaster archer can shoot about 7 arrows a round with improved haste, 2-4 arrows are usually enough...each hit will cause a dice roll, and if your roll beats the targets save...poof!!!