With great gear you can sit at >40k hp with a good armour value and great dodging (since your dex increases your dodge) that with your escape spells a DH shouldn't be struggling anymore than any other class in inferno.
In replying this I'm not claiming that DH struggles more than any class, but is 40k HP really feasible, while maintaining decent DPS? (I.e. above 25k) There has to be a trade off somewhere and I feel somewhere around 30k or less (to avoid getting one shot by everything) is sufficient.
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