Devastation evoker does not have anything unique, compared to augmentation and preservation.
Changes in 10.2:
It takes 4% less magic damage and does/receives 2% more healing that the other 2 specs (the last patch buffs), but only if you drop a few talent points to go into these
It no longer has strong burst - mastery was nerfed by 25% and augmentation burst is now stronger that devastation burst.
Devastation has better consistent damage, and better damage at low enemy health levels, compared to before.
So is that it? Less burst and more consistent damage, but with no added utility/survivability/advantage?
The only thing devastation had over the other specs was the burst. Give the spec something to differentiate it and make it desirable