So i've done a lot of AOE farming using Frozen spire at 40 and I'm almost certain the move is bugged. I believe that you are taking durability damage Per tick or damage per mob every 6 sec.
So when i've pulled a group of 12 mobs together, used Frozen spire on all of them i'm taking durability for the initial hit (assume this is intended, it would make sense.) I'm then however taking durability damage for the next 6 seconds (1 tick per second per mob ) due to the bleed effect.
This is causing my Weapons to break in about 30 minutes of farming (non stop,no downtime) yet leaving my armour hardly effected.
Perhaps this is intended that you take durability for Damage over time moves, if that is the case I feel it needs to be toned down slightly.