It's not only that fights are short. I don't think fight length matters at all, actually. It's that mana pools are huge, and glyphed Mage Armor plus Improved Mana Gem plus Master of Elements means I never have to dip below 90%... which then means I'm always maximizing the return from Arcane Mastery.
I think (hope) that will level out by the time we're entering Cata raids, but we'll see.
I think (hope) that will level out by the time we're entering Cata raids, but we'll see.