A word on INT mages.

Increasing Mana Shield duration does not help effectively in PvP- it definitely merits an advantage in PvE though.
But since we are talking about PvP, the only possible changes I see that actually boost Mana Shield's potency is a higher armor buff or lower cooldown time.
Having a longer duration for MS doesn't apply when most mages end up getting their mana drained from a bear combo or simply have their shield blasted by a bird.
The better solution as suggested is to increase the armor of Fiery and decrease the damage output of bears.

To be honest, the skills for mage are not what needs improving, at least not at endgame; it's simply that mage's INT endgame set ultimately loses out against all other forms of combat in endgame PvP.