The problem with being so tanky in PvP is that, appart from 1v1 situations where you can never die, you're not going to be able to help much.
With the current 3v3/4v4 score-based PvP model, if you aren't killing, you're probably not helping your team a lot. Unless you've got mostly CC, and it's ok to have tanky-cc builds/characters. And even then (if you plays moba games) you know what happens to tanky-cc heroes there: people scatter, avoid them like the plague and kill their allies
Look at that DH. If people with 150k dps will have trouble killing (due to armor and resists), his 20k dps is probably 100% negligible. You could let him hit you for 30 seconds and he still wouldn't kill you, so you just throw your spells at other players and avoid his cc.