If you plan to push M+ blood DK will never be even close to competetive because of the class design.
The lowest physical damage mitigation out of all the tanks makes us a not viable option past a certain threshold.
While fine or even great on mid keys the higher you go the worse it gets. I don’t think blizzard will even buff us because then blood DK will outshine everything else in raid scenarios where we are currently good.
I redesign of the class would be necessary which will never happen this expansion.
I tried starting with my blood DK who i stuck with since Legion but now since i enjoy M+ the most i think going another tank is the best option.
Im going to stick with Blood, I enjoy the playstyle regardless and I dont think its so devastating that you wont be able to tank m+ at all. Should be fine pushing weekly +15 at least when we are geared up with a selection of legendaries. Besides balance changes could happen at any point and the new tank you play because its strong now might just get nerfed down the line.