TBH, I think it is better for mages, since we use DD and DoTs whereas they use DD spells almost exclusively. The nice thing about the Ephemeral Power thing is that you can slap on your DoTs, and then activate it and enjoy the added damage on all DoT's / targets for the full 15s. This one however has a maximum use count (280/35 =

and hence is better geared for DD spells (and superior for those).