Mages only have 1 truly dedicated Keystone...
Summon Aery is really a support keystone that mages happen to be able to use.
Phase rush is meant more for bruiser but this guy likes it
cause nothing else is good on him.
Only keystone that was truely designed for mages is Arcane comet.
On the flipside, ADCs have 3 dedicated keystone, and Assassins have 3 dedicated keystones. Tanks have 3 dedicated keystones, and even supports have 3 dedicated keystones.
Bruiser apparently have phase rush and conqueror.
I'm not saying mages can't use the other keystones, I'm just saying fundamentally from a design standpoint, mages only got 1 keystone that was designed just for them, while all other classes got 2-3 keystones designed for them.