You can level really quick if you keep up with side quests, so I can see the annoyance of people not having the right gear for lower level dungeons. But is it really that bad higher up?

I only ran into such a thing once, where the tank in DD had level 20 gear for some dang reason. I ended up leaving the group, since I was the healer and the 2 DPS were friends of the tank who could apparently do no wrong in their bad gear.