Yeah well maintaining optimal DPS in groups as a tank also depends on how freed up the healers are. I mean if you got people dying to megaflares even occasionally or just people taking unnecessary damage then that's a DPS loss for the tank because tank's gotta mitigate with stances due to healers being too busy trying to crutch the raid. PUGs are all unknown players who may not perform necessary enough for the tanks to hit that optimal DPS. The more distracted healers are having to heal / ress unnecessarily the more tanks have to mitigate so I would say to achieve those 'excellent' or even 'average' numbers the tank's performance is at the mercy to the rest of the party's performance.
With that in mind, is judging tank DPS in PUG groups reasonable?