Tank Mitigation vs Tank DPS.

[IttyBitty]

If you are not saving me actual healing GCDs (as opposed to theoretical GCD savings from cumulative tenacity mitigated hits) then you may as well have just filled your gear with Perception for all the good it does for me as your healer.

Damage in this game is spiky.
Regens and embraces are pretty much always rolling so incidental damage from AAs are pretty much covered until the next big hit comes along and demands attention regardless of how much you're Tenacity mitigating them.
I am going to heal you for 45-50k regardless of if you take 46k damage or 40k damage (because that's how much non-crit Cure II/Solace + Tetra will heal you for).
It will take the same number of GCDs to heal you to a safe place after a 100k hit as it will to heal after a 90k hit.

One of my former static tanks used to maximize tenacity. I didn't notice any difference between when he did and when he didn't.

I personally think all substats are pure garbage because the gains on them are so small, but I'd still recommend you Meld DHit, Crit or Det (and Spd if you're trying to hit a breakpoint) if you're trying to optimise, because pushing phases and clearing faster are more important than taking a little bit less damage. Any of them are "better" than Tenacity as far as I'm concerned. Hell, meld Tenacity if that's what you really want, it really doesn't make an iota of difference to me. But acting like you're helping me or any other healer by doing so is patent nonsense. You'd help me more by rotating your cooldowns properly (and bothering to use Arm's Length as a cooldown during trash pulls) because most tanks don't.