This would just be a warning for responding to a question where the answer is in the first post of the thread: "Optional, useful for untanked targets." However, you've been warned before, and moreover the answer you've come up with seems like you forgot about tanks abilities altogether.
I have no idea if the automatic NV-slow does have a chance to proc missiles, but we usually expect some kind of evidence posted. It should be possible to make a calculation to show what dps value this has if it is true, and show some combat logs as evidence to back up your statement.
Originally Posted by LelĂ¤nd
Mage Talent, Torment the Weak: Your arcane damage spells deal 6% more damage to snared or slowed targets.
I am starting to see less and less mages spec in to Nether Vortex (2/2 Gives your arcane blast a 100% chance to apply the slow spell to any target it damages if no target is currently effects by slow) for the ability to pick up some movement talents.
Who / what else in the raid puts a continuous snare or slow on the target? or are the mages who do this manually applying slow?
Even if you put 1/2 into Nether Vortex you should still almost never have to manually apply Slow.
Slow lasts 14 seconds and if your Arcane Blast is even at a 2 second cast time (which it should hopefully be under), then with seven AB's you have a...94.5% chance to at least get one Nether Vortex Slow in before the Slow debuff timer runs out. Not to mention any Haste buffs you'll get and AB stacks reducing cast time.
I personally keep 2/2 Nether Vortex for the chance that NV-Slow will proc Arcane Missiles during my conservative phase to make it smoother.