I’ll use warrior as my case in point about damage in regards to m+ dungeons. Warriors are currently pushing well past 20+ in terms of m+ dungeons. Their survivability was recently buffed enough (think it had to do more or less with some defensives being taken off GCD) for them to be put on par with BrM, Prot Pally, & Blood Dk. The difference though was that they do more AoE damage than all other tank classes. At the end game, when survivability isn’t the biggest issue but time (m+) or every ounce of extra dps matters (heroic/mythic raids), a group or raids needs will change to want a class that can dish out the most damage, but still survive.
I thought Vengeance would be that tank class everyone regards as bad until endgame where their damage would outpace the need the survive. I had hope Blizzard would give them a buff to demon spikes or some extra CD for that bump in survivability. I don’t mind where DK ended up, I mind that what’s going to matter for MDI and mythic raiding in the future is going to hinge more on how much damage output a class like warrior has!