Fucking mmo/dota mentality should die.
Competitive balance is an issue but those two specifics are hardly the same.
The issue with DPS is that it implies a world in which damage dealing is a drawn out race with carrots on sticks.
The issue with Tanking is that it implies a world of threat mechanics.
The issue with healing is the same as DPS, except on the verse.
Those are all specific issues with MMOs and the best encounters in WoW were those that fled from the conventions of boring steady DPS, Healing and, God willing, Tanking. In Dota, damage dealers are about opportunity and burst damage; 'tankers' are only hard to kill and healers fill more specific support roles of which healing is only a part. Its also unlike WoW where healing can't really save you from a barrage of attacks. And that is fine for a combatfag game.