Focus on the elemental spells, and nab the fire and ice weapon coating spells if you can.
And once your mages can just walk around like your tanks, even the other two dragons in the game aren't much of a threat. Mage/Arcane Warrior/whatever else - AW allows mages to use their magic instead of strength, which means you can deck your mage out in plate/massive plate without having to waste millions of points in giving them something to wear.