That's a product of overgearing. In 475 gear (around what early groups had) you couldn't do anything near negating all the melee damage. So the constant stream of damage that we can heal ourselves through, but not others, plus the adds' lasers and Gary's shadowy attacks that we had nothing for set up the perfect storm for burst damage, and DKs having the worst passive mitigation made them that much more susceptible to all of it.
10H had its own issues in progression though, with adds gibbing people. With fewer targets to pick from, it's just a matter of time until 3-4 pick the same person at once and smash his head in. That's hardly our fault.