you’re playing at a difficulty level that is too easy for your gear level. That is why this is the case. What you’re describing is the difference between classes that can unload their burst in 3-4 GCD’s vs the typical caster that needs 10-12 GCD’s to get rolling. If you get to a level where the enemies are living long enough for the mage/druid/dk CD’s to run their full duration the damage will even out drastically.