For starters, you're falling into that old trap of people comparing a spec to a class. Putting that aside, 50% shield wall and bear form, + shifting to escape outweighs any short term defensive abilities a dk has vs melee cleaves
Death strike drops all my pressure too
You haven't seen them die through heals yet because of death strike, plain and simple.
At the end of the day, nobody is suggesting that death strike is fine. The point is, while it may be OP, it's *all we've got* to survive melee trains.