*EDIT* just realized this is a necro thread! I'm adding my two cents anyways :P
I see the appeal of all-mage groups but it's just so boring in its finality. It's extremely efficient, since you can make identical macros on each mage and program your keyboard to hit the same macros in each windowed instance at the same time. Even if you don't do that, just get a monitor big and roomy enough to put all windows side by side, and alt tab through each one hitting the macro. Once you have this group, you could add a shaman for buffs and slows, but he would be an odd-man-out and would, probably, end up standing there uselessly quite a bit. You could add a melee but then you're managing heals on a PC... You could add a bard for ADPS but he's taking up a group slot and is he providing enough for the xp he drains?
After making a group like that... I can't see wanting to go back to a traditional trifecta group (well, fourfecta, in this case). Why spend weeks and months training yourself to manage four different classes, when you can load up on four identical classes and go to town with one I WIN hotkey? And since no other class does it better or faster, Magician is the class to pick for a foursome in today's game.
That's the finality that I would want to avoid, because once you go down that path I can't see you wanting to adopt a less-efficient four box group than the four mages, four pets, two healer mercs... It's like when you learn to charm kite as a Bard, and then after experiencing that sort of XP gain, you go back to meeleeing with your healer merc, and the kills take literally forever, and you gain 1/50th the xp that you would get from a quick swarmkite session. You can't go back after that. Anything less than swarming is less efficient and more time-consuming...
Edited, Feb 5th 2015 12:09am by xlitin