Blizz has a different definition of "viable" than players do. GC's Dev interview at the start of ToT pretty much confirms this. As a long as a spec performs well enough to not get sat, Blizz doesn't care if its dps is not good. GC has even said that players care too much about performance. Will Frost or Arcane be as good as Fire next patch? Probably not even close. Will Frost or Arcane be just good enough for progression? Probably. They simply don't care to make all the specs truly balanced. That's true for every class.