DK's seem to have a lower health pool by default than other tanks (Frost presence used to be huge, but got nerfed to hell), and ofc no block rating. Priests specifically offset this with preemptive heals, hots and a huge stamina buff.
I'd agree that DK's are relatively the worst main tanks right now, but they make fine offtanks, and even as 'relatively bad', a properly geared and specced and played DK can breeze through any 5man. The problem you're noticing during levelling is that dk's start at 55, and anyone whose never tanked before, who rolls a DK to do so, isn't going to have the 55levels prior of experience levelling up. I've seen 'tank' dk's trying to tank in blood presence, for example. It would be the same as handing you a level 55 healer class to someone whose never healed a thing before, and watch them try to heal instances in their levelling dps spec.
A level 55 warrior is going to know more about tanking than a level 55 dk. That's just how it is. Personally i believe dk's should've started at lvl 1 like everyone else.
