I would have to disagree again, The player base just doesn't allow for it these days. Not everyone has the time or want to roll a second character just do another role. When you look at the classes now they are either DPS/Utility or Hybrid classes and this has been intentionally done to ensure that the player base stays interested and doesn't feel like its a chore to full several roles.
Look at the decisions made and you can see that it is a common trend. BC both factions got their opposite factions hybrid class, WOTLK released a new hybrid class, Cata allowed more race/class combos, Pandaria released a new Hybrid Class. I honestly believe if there was a viable way for them to do it the current PURE dps classes would get some sort of hybrid.
But going back to the original arguement I do not see how you can realistically say that a Warrior dps should be lower than a Hunter dps by a fixed amount simply because they are a hybrid class as that simply does not make sense from any point of view other than for stroking the egos of those that are still considering themselves as a pure dps