I can't speak to other DPS jobs, but as far as black Mage goes... I don't know, sure crit involves some luck, you can maximize chances with gear, but thundercloud and firestarter, luck involved too much, could make a Mage great or worthless in some fights.

I say this just because, I'm not sure it's fair to stick the tag 'play the job right, dps is fine' on it. As it is now, just a little luck and can spam 6 thundercloud in a row and double the dps of others, or you could get none. You could go an whole turn in coil without a firestarter.