Doesn't matter anyway...
Even if it is casual content it doesn't warrant it. Unless it's Relict/Emerald (Or you're a Raider) you're likely going to be Ilvl capped in the Dungeon/Trial and rotated cooldowns are strong enough to mop the floor with wall pulls. Dungeons is you wall pull > pop rotated cooldowns > Get low HP > Healer Off-Gcd heal > Repeat. Getting targets killed much faster will save a lot more HP damage vs trying to reduce it more this is illogical and Tenacity will not do this for you, roughly 10% reduction is really bad. And if you get a Healer who spams GCD Heals, my friend he is a Healer who is ignorant, or listened to Mentors awful advice.
The only trial who puts the threat in Tanks was Thordan Ex back in 3.1 and he was a comparison to Savage raid, everything else are extremely lenient.