IAs it is, as a mage I'm nearly useless against level 90 mobs in PvE; certainly I stand no chance against more than one opponent at at time in PvE. On average, my spells do 30k damage per hit; most level 90 mobs have upwards of 400,000 hit points; so it takes roughly 13 spell casts to best a level 90 mob. I find it difficult to believe that this is considered acceptable.
Has Blizzard forgotten that mages wear CLOTH armor? Have they forgotten that mages are not meant to absorb damage?
I counted 11 spell casts to take down 1 target, waiting on procs, but my gear is slightly ahead of yours at about 476. That's spells which take a few seconds to cast too. An eternity when you're a class that wants to destroy targets at range before they ever get the chance to lay hands on you. Sometimes I get proc's and can burst targets down in 3 or 4 hits. The PvE game feels really good when that happens, but its not often enough and involves the use of cool downs.
What helps is Ice Barrier - it absorbs most damage incoming from 1 mob at a time. In MoP, I have to expect that melee targets will hit me for 30 seconds or longer.
What drives me is when I try to kite but pull additional mobs. There's been many times that I have to escape the fight since I don't cause enough damage to finish them before they'll finish me. Some areas in the dailies are dense, and if there's nobody around to pull the additional mobs I abandon the quest.