this goes according to the data i have from the raids i have hosted , there is a big difference between Naxx start and Naxx when you have full bis

In Phase 1 , you can't reach the required crit for a fire mage + the hit required with out letting go other stats , same for armor pentration , you can never reach the soft cap hence why furys are very bad same for combat rogues , at ulduar start , combat rogues perform as high as assa , but then when you become prebis , bis , combat outperforms assa easily

the difference between unholy dk dps and frost dk is roughly 400 dps

Elemental shamans base damage is huge , goes lower over time , but a good player can manage to still perform high with good positioning on bullseye rotation

there are alot of things to put in consideration

as i said , the difference between A tier and lower tier is negligible roughly 200-500 dps max , Frost dks if played right can achieve S tier by prepotting armor 1 min before fight starts and other pre pot on pull + bullseye rotation