It goes a little beyond that, as the arcane blast debuff only affects arcane blast. Essentially, arcane blast is the highest sustained dps (but unsustainable in terms of mana), followed by arcane barrage, followed by arcane missiles (which is very close to arc barrage in dps, and free of course).

So, from the standpoint of a boss fight arcane is less about a constant rotation, and more about optimizing your mana bar to the fight you’re involved in (with a little rng in the mix). (Source)