I believe the idea is, you tank with your lead mage. Mages have surprising mitigation to physical DPS. Frost Armor/Ice Armor slows melee attack speed by 25%, combine that with 20-25% mitigation from cloth + say a defense(armor potion), and your real physical mitigation on mages is going to be in the 45-50% range. The issue is HP pool.

So, lead mage runs in with shield, and then you just go ham. Everything on the mages gets its melee attack slowed, and you burst with your aoe dps.