And, what Criminal said about his lvl 73 mage doing 100dmg on 130 mobs,
well that was just to annoy u, 113 dmg on rag with firebolt

well anyway, just as i said, theres a lvl factor on mobs, even if u can hit up to 5k dmg, if the mob is much higher than u, u will barely hit
i lvl at 170-174 bolgs room, i started there since 167-168, my dmg on the 173-174 ones was like 1.2k max with skill+shatter at that lvled, when i lvled to 170, it got back to 1.7k-2.3k dmg per skill
altough, 200 dmg is still bit odd to me, im pretty sure u hit higher than that, never tried but still way too low for 16 lvls difference as a mage, but maybe im wrong.
try to lvl at mobs around ur lvl