We are not "insane" on any affixes. Sure, we can push like 1m overall in certain dungeons and affix combos, but there are very few classes that can't. We are not dead weight at all, but 90% of classes at same skill level will do more overall damage than a shadow priest. That being said, a lot of the reason we fall slightly behind on overall damage is the packs with low health targets, which really aren't main priority at all. This makes us look better in dungeons that lack these mobs, i.e. DhT and NL.