The biggest problem with 1-80 dungeons is heirlooms. It is nearly impossible to tank them because you always have someone doing insane damage.. but it really doesn´t matter since that dps can also tank and kill the mob also. It is sloppy gameplay, but it isn´t that huge of a deal. The problem with heroic 5mans now is that as we outgear them, we also get lazy. I am guilty of this myself. I rarely mark targets any more, so if a geared dps focuses on something that I am only hitting with swipe, yes he is going to pull. But it is not something vengeance should ever be able to fix because it means I will be doing insane amounts of damage (if my off-target aoe can keep threat from a geared dps´s focus fire, that means my overall dps is huge).