I do think pures should be ahead, yes. The hybrids could have a slight (noticeable) advantage in mobility, suitability etc.
Even if a Warlock would be designed to do 5-8% more damage in a stand still fight than a Priest, the Spriest could catch up in a real encounter, with his superior move/cast abilities, or being able to stand in the fire for an extra 3 seconds because of great defensive cooldowns etc. (obviously, it's pretty much the opposite right now).