You say mages suck against bosses, but that definitely isn't my experience.
Many bosses have elemental weaknesses. Warriors can't take advantage of that - mages can.
Mages can spam cc on the boss, turning them into a harmless punching bag (and yes, bosses can definitely be cc'd). Warriors only have access to one hard cc (knockdown), and only two abilities which can inflict it. If the boss has high Bodybuilding, your warrior is up a creek.
Mages can weaken the boss (soul sap, lower willpower, curse, weaken, etc)
And, of course, Mages make the warriors twice as good. Oath of desecration, elemental shield, bless, haste, etc...
Mages were the MVP of my team from level 1 to level 21.
