Yes because the math shows that with any kind of moderate haste setup, any DRK with DB merits can effectively zerg 10,000HP off of any monster and the nice thing about it is that they can do it while eating tough TP moves because 1 second later they're at full HP again.
For completely elite setups, you're gonna see a KC outperform them all, followed by a BZ (though debateable, and slight) and then RC. A DRK can only cap at 22% haste anyway and at Lv.72 you're not going to sacrifice accuracy for a blitz ring, so let's just knock off that and homam pants now and make it 18%. At that haste percentage, I can't recall the math (Hint: Read the Advanced forum and search it) but it may be the breaking point for being better than RC...(Note: 18% is assuming that you have both Dusk+1 Feet and Hands and V/S Belt)
Earlier, the every 6m comment refers to the fact that a KC DRK is able to zerg every 6m for 1m while being Cure bombed, since he can use shadows to not be hit, regen HP through BW (Though smaller since less per hit damage is dealt) and lose less HP per swing making Cure bombing more manageable for healers.
In any event as a DRK in and end game LS, you should always look at what gear you have available and use what suits you best and you should always be able and geared to zerg. It's what we do best, sadly, but it's hella fun.
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