Originally Posted by
Mammoon
The job of a DPS is pretty much the same every fight. Outside of perhaps a single target rotation and an aoe rotation, there isn't much else a dps can do on a typical fight.
The job of a tank or a healer generally varies fight to fight. Bosses are different, debuffs are different, damage is different. While tanking can be generalized as "tank the boss and/or adds, face them away from the raid, use cds for big damage," it still varies some. Healers have a general rotation (in the sense that some spells you use more than others, and you play a healing class long enough, it becomes pretty standard) as well, but it is much more dynamic than a dps's, because it changes with every fight, and it potentially changes a little bit every time you pull a boss (due to RNG with damage).
As it has been said, you typically have many more DPS, so often their contribution isn't looked upon to be as great as a tank or healers, but bad dps make a fight a lot harder for a tank/healer, as good DPS make the fight much easier.
As far as PvP goes, I have played both a dps and a healer, and it is very much a toss up imo. It is often hard to find a truly good healer for arena, but the same could be said about DPS.