I don't think it's too much to ask for to have a pure DPS class have at least two specs to choose from for PvE or PvP. Right now, well over 90% of raiding mages go Arcane, partly because they're ignorant and don't realize that Frost is a viable raiding spec. Fire is only useful for Alys, otherwise it just doesn't measure up.
Frost is fairly decent, it sims for roughly equal damage to Arcane once you have 4 pieces of T12 and provided the Arcane mage doesn't have a Shard of Woe. But it still has a lot of rough areas. Our AoE is nowhere near as good as Arcane's, and Blizzard is a major pain to use. Lots of other dps classes have a movable AoE, but frost doesn't. Shadow Priests have Mind Sear, locks have Hellfire, Arcane has Arcane Explosion, Boomkins have Starfall and mushrooms, etc. Not only that, but because of the way the Arcane mastery works (mana adept), Blizzard actually does more damage as an Arcane mage than it does as a frost one.
On top of the AoE issues Frost has, there are huge discrepancies between our burst damage and normal damage. I'm sure Blizz is probably worried about buffing frost damage because they don't want to make it more OP for PvP, but I would completely support a nerf to burst damage in exchange for a buff to sustained damage. Hell, there's been more than one occasion where I've started out a fight doing 30k, but by the time it finishes, I'm down to 18k or so.