Tank Mitigation vs Tank DPS.

[Adrestia]

By far the most defense you get out of gear is from the physical and magic defense on the left hand armor. Maximizing your item level is the best way to maximize your mitigation, since gear of a given class (plate vs leather etc.) will all have the same defense at a given ilvl.

This was true for a lot of WoW as well. I could trivially tank heroics in WotLK as an arms warrior because of my passive armor stats being basically as high as a prot warrior.

As far as tenacity, it’s not that it does nothing on paper, but that it does close to nothing in practice. Even raid boss autoattack damage is mostly covered via regens and incidental heals coming from AoE healing the raid. So for that constant trickle of damage, you’re just turning a chunk of the healing into overheal. It’s not like you’d ever get enough TEN that your healers could skip an entire cast. For actual tank busters, they tend to fall in classes of “a healer will actually have to cast a GCD heal on me” or “I should use my invuln on that.” Some of them don’t even meet the threshold for the first and an essential dignity (btw welcome back to the game ASTs) or similar will top you off on its own. But they’re really not “if only I had 4% more mitigation” scenarios very often. “If I only had 20% more” sure, if you misalign your cooldowns. But you’ll never get 20% mitigation out of TEN.

E: tenacity isn’t reducing incoming damage by 1% per 100. That would make 3000 tenacity a permanent Sentinel buff. Tanks could skip using cooldowns entirely and never die.