I orginally agreed with the OP a few months ago, but after thinking logically it is simply amazing. Ofc it isn't a +dmg talent but do we really need it? We don't need a CD now we have a new spell and dps mode (DAA+Mindspike).
Mana was never a problem for me so I used it exclusively for the damage reduction 99% of the time. It allowed you to ignore ALOT of one shot boss talents especially in ICC and on a 1.25 minute CD glyphed it is the best survival cooldown in the game.
The whine about it being casual vs hardcore is moot, while casuals will use it to "be bad" an advantage is an advantage. When there is progression in the mix survival is key learning new deadly mechanics and some times 6 secs of living can be a kill.