The other problem with even playing offensive mages or magic damage dealers at all is that you have to look at the fight like this..
The enemy has physical AND magical armor, so you get the magic armor down, but you are going to do so little damage to his hp compared to your 3 other melee dps why even try to do magic damage in the first place, which is why right now its best to play 1 support mage and 3 melee damage dealers, also the fact that the mage is primarily if not only aoe abilities that will kill your rogues, tanks and close range fighters.
Overall the mage in general needs to be tweaked, though I believe Swen said they are going to add more spells into the game to test eventually, so there might be some good single target spells that'll make an offensive mage more viable.
