The thing is, DRK isn't really in a position to forego TBN. I suppose as an OT you wouldn't need to use it, certainly not as often, but as a MT they don't have many mitigation options without it. In the grand scheme I don't see an issue with having a cost/benefit like this, WAR is similar with IB - good mitigation boost but comes with a dps loss. Obviously War's kit without IB is better than Drk's kit without TBN, a separate issue altogether, but in general I think trading dps for mitigation makes some sense.

Maybe Bloodspiller should just be off the GCD? Though that doesn't exactly help the problem of excessive dual-weaving.