Why Crit for tanks?

[Carighan]

Also tank survivability is a 0-1 problem. Lets say we are introduced to a problem where both tanks are spent out of their cooldowns and boss enters a phase where it 2-shots tanks with the auto attacks, but a certain amount of tenacity makes it a 3 shot instead. What would happen is the tanks would meld exactly the amount of tenacity needed for that to happen and not a single point more, rest would go into damage.

This is also why it is inherently problematic for the tanks to do more damage when not focusing on using GCDs on defense (which they can't in this game, so let's assume 100% is spent on damage) than when the healers are doing the same.

You need for tanks to want to make the healers heal less, because that's a gain in damage. But it isn't, tanks gearing for max damage is more efficient overall.