the much touted control of frost is something that happens as a by-product of frostbolt spam. with a 2.5 second cast time, you will have absolutely no control if you must be mobile without wasting your valuable frost novas. in pvp, managing your frost cooldowns is the only way to win, and by no means guaranteed even if you're facing a snare-vulnerable class (shamans and sometimes DKs). classes with a means to remove magical effects from themselves, or who can become invulnerable to your movement impairing effects (paladins) you will be absolutely useless as anything but a decoy.
the requirement that deep freeze target something that's already frozen makes it situational like very few abilities in the game. because of cast times, you will mostly miss out on big damage opportunities and instead be restricted to ice lance spam. the game has changed. even with a severely nerfed pushback mechanic, mages cannot afford to stand still to cast anything.
arcane has almighty single-target control via the instant-cast slow, PoM and arcane barrage (another instant, but it can be a main nuke with its 3 second cooldown). because you can choose when to unleash your arcane power in combination with missiles and clearcast, arcane has just as much on-demand burst as frost. if not more. i might say more because, unlike with freeze effects, the opportunities to use your burst depend on your own timing of the situation, not merely where you're forced to use a nova just to gain space.
and you can't just trinket out of an arcane power...