I agree with OP. If tanks can wear most of DoM clothes (Yes, there is DoM-specific armor, I know, but just look at all the mage class crafted gear, any class can equip that), then mages should at the very least be able to prism things such as shirts and tabards for glamour. It's all very light gear, and hell, if an archer can run around in a robe and not stumble, I don't see why a mage shouldn't be able to be moderately clad in armor as it fights.

Glamour is a purely aesthetic feature, it shouldn't be something that implied class restrictions.