True, but as a Blood (or even as Frost if you go back as far as Wrath) tank I could also outdamage most other tanks at the same time as doing all that... WoW tank balance has some weird weighting to utility, and on the whole, far from the tightest of parity.
I agree on all other points, though. I should have been more clear in reference to just the idea of changing out a set role slot, e.g. the choice between a Protection Warrior or Blood Death Knight or Guardian Druid. When more slots follow from the consequence of a tank change, then rDPS is always the lead concern.
I don't think that's true at all. It's frequently the issue, but as in the WoW examples you've just made, may not even make up a majority of cases.
Pretty much exactly as you said just above, but just giving my own experience here:
In Cata and Mists, I considered Blood OP not because it's damage also happened to be ridiculous, but because unless my party was incapable of interrupts and CC, I wouldn't bring a healer to speedrun dungeons. Because healer damage hadn't yet been raised to anything consequential, they just weren't worth having. The rDPS value of my healing, therefore, was tremendous. I could do blue DPS damage, yes, but I could also allow for another orange at the cost of a grey, all while making things easier for my party than any other tank could via Deathgrips and AMS.
And then I went and did the same thing with a few other tanks, even if not quite as easily. Some needed a Ret or Feral, but Feral's healing was a HoT and thus easily made early or late and either that Regrowth or Ret's Flash of Light took up only an open GCD (i.e. one they had no resource to do anything else in anyways). In each case the majority of the ridiculous power found in tanking came down to self-sustainability, not damage. And 12 years of frequent WoW foruming's worth of anecdotal evidence, alongside some statistical compiling thereof by certain in-depth threads on the subject, indicate that self-sustain (be it a lack compared to previous expansions or an overabundance that forces out healing specialists) is the lead controversy surrounding tanks, not their direct power level. At the upper end, WoW tanks have rarely had the relative throughput our tanks enjoy except in AoE alone. XIV tanks don't scale as well as DPS, but WoW tanks scale even worse over time.
I feel like this is where we such discussion could use some delineation. There is activity, and there is capacity. The capacity of tanks may be too high, but at the same time the activities of tanks can be too few or shallow.
For instance, I'd like to see the capacity curtailed a bit in the ways that can bring into use (new) breakpoints in compositional or tactical decisions, but at least cost to sustained value, while enhancing the quantity and quality of tank activities.