Do you have Rush Attack? Even 1 skill point invested helps against mages a great deal. As soon as you can target the enemy you can fire the rush attack to at least plant yourself right in their faces if not do a nice chunk of damage and knock them over.
But it basically teleports you directly to their location, which limits the amount of spells they can fire as you close in, and also keeps the melee types from taking whacks at you as you charge toward the rear ranks...
Its the kind of ability that benefits from pausing, then targeting then firing to make sure you rocket towards the right enemy.
They may still have a load of HP but at least you've got a head start...
Leveling charm isn't a bad idea either, - charming mages and archers is a great way to eliminate them from the threat environment while you deal with the more mundane types.
Charm shaman/healer types for free healing too...
