Personally I suspect they just blanket threw armor nerfs on everything that has a ‘DPS’ role available with high armor, to save themselves the effort for having to adjust it based on spec and work in an extra line of code…
Only having to adjust it afterwards in a second patch because it was just so crude it caused too much problems for too many people, that they felt forced to put in ‘some’ work.
Probably thinking they need not bother with creating difference code for feral and guardian Druids, because they’re just irrelevant and it was easier to just nerf the entire bear form for everything.
Ironically for Guardian/Feral druids, Moonkin form still gives 125% armor in PvP, which according to the patch notes should be 100%.
So that is bug, but it’s a bug they don’t fix, because they don’t care because it’s not relevant for those druids. I’m just bringing that up to show they’re just doing whatever is less work for them and not really having a plan to it….
I think they just threw Tank specs under the bus as part of that, since as you as say they already receive bonus damage to everything AND now also take more melee damage on top of that, instead of adjusting that bonus damage for specs individually.
Hence why DH and Brewmaster did not receive any ‘extra extra’ damage, because their DPS tree does not have high armor and in the eyes of Devs the DPS spec is the only thing that matters. Since Tank already took that extra hits and it wasn’t really needed.
So your Blood DK got an extra armor nerf because they didn’t want to bother to adjust it for each spec. Likewise DH got to keep its extra armor, because for their DPS spec the nerf wasn’t needed. So pure laziness and not caring.
Yesterday they published they were laying off another 1900 jobs, including those in Activision. I would not be surprised if it was related to that and quality control took a huge hit.