Because getting hit for 196 instead of 200 is such a win. Getting hit for 160 instead of 200 when it counts is a bad bad bad, worst survival. And Vampiric Blood is not good at all. Better is 20% more armor that you can use only against phisycal. Or unholy, where you get 20% damage reduction once a minute for 6 seconds - Best is to wait that minute before each pack pull, so you can double it and get 12 secs - that definitely increases speed of party, you might even finish it today.
27% overall is RNG, which will bend you over.
And please give names of those bosses who do that constant dangerous magic ticks. Because I encountered few, can count on one hand.
Sorry that wont help if every dps is attacking different target. If they are damaging same target blood can get the job done. Even mages with living bombs are ok. And you forgot, unholy boosts magic damage, so it boosts threat of magic dps. And that epic Frost snap AoE threat, yea nice, because 64lvls have such imba burst oh my.
I don't know where you have tanked, maybe in some sims or something. But you are spwing horsecrap and its far from what actually is happening in dungeons.
Go do some dungeons and see how many times you will actually need 3x Death Strike.
Just stop, its embarrassing. I can recognize best tools to get the job done. And blood provides plenty. Of coarse it is possible to do with Frost and Unholy. It is possible to do it by spamming IT and never using any other spell too.
Just remember each time you die, you could have probably pulled trough if you were blood.