That chart shows that Blizzard have been largely successful in closing the gap from top to bottom. It's interesting that MM appears to have stayed level when this is known to not be the case, perhaps the small sample size and AoE-heavy nature of the SoO fights is limiting it. I've had good results on Iron Juggernaut (normal) and reasonable results on Dark Shamans (lower dps than SV but Concussive Barrage is invaluable in handling the adds while we learn the fight).
What will be of particular interest is how close everything is once people have mostly SoO normal/heroic gear. We already know that Hunters historically scale poorly, I predict we'll finish the expansion as middle of the pack which is OK provided the "pack" remains as close top-to-bottom as it is now.