Because said Prot Paladin is in a guild that doesn't let you exclusively play one class and also has multiple top-100 Mythic parses on his Blood DK?
Look, I'm fine with people offering their opinion on stuff. You don't necessarily need to be an expert, but there are things like Blood DK and issues with RP capping where you sort of need to have hands-on experience with it to understand just how bad it is. You're incentivized to stack a stat that basically does nothing but make you waste resources unless you play with Breath of Sindragosa. That's why it needs to stay. The fact that it's an example of the sort of gameplay ALL tanks need to be compelling (i.e the ability to smartly make a tradeoff between mitigation and DPS) in high-end content for good players is why it's also relevant to BrMs. BrM being the most "modern" of tank classes you sort of don't suffer from as many of the old, weird design flaws that many other specs have (but then of course suffer under the fact that the devs literally seem to not understand how you work) - something like ChiEx is essentially an analogue in terms of what it offers gameplay-wise to BoS, presupposing of course that it's not just the highest-survivability choice like it might be in 6.2 because they're dismantling Serenity.