The point of essence of magic is the mana regeneration, not really the damage. It's an essential talent for my prophet build, but I am not sure about it for a mage because I don't really run dungeons with people when I spec to mage, so I don't know if I have mana troubles or not. It could be one of those low tier skills that are there for prophets to pick up.
However, I am sure you can make use of it if you find yourself using normal ranged attacks in between skills. If you spend all your time AOE farming/grinding, then I don't think it's that useful.
Edited by ComradeLewis, 04 May 2015 - 23:33.