I actually posted a request that they have tenacity scale off vitality and posted something similar to what you said on the tank role forums
This is a pretty huge assumption considering just how many tools we have to mitigate things right now
Feint/Addle
Apocatastasis/Palisade
Sacred Soil
Astro Shield
Adlo
Divine Benison
Intervention
Passage of Arms
The Blackest Knight
Reprisal
Eye for an Eye
The Bole
And this is just stuff that other people can do to the MT or the boss. If they really need to stack up mitigation they can go WAR(mt)/PLD(ot) and abuse intervention, warrior CDs, and Cover+paladin CDs. If there's a super dangerous and hard to compensate for cleave you can just slot in VIT pieces as needed.
They basically have to role lock pre-Stormblood gear. There's no other solution if they don't want to change SB accessories to have strength or change how tank damage works.
1) 1000 points of Tenacity is about a 5% dmg reduction.
https://www.reddit.com/r/ffxiv/comme...city_datadump/
2) Taking just left-side in consideration, melding 520 points of Dhit translates to a 14% proct rate, aka about a flat 3.3% DPS increase. Meanwhile 520 points in Det = at least 140 attack power (at least in patch 3.5?) which is a 5-6% DPS gain for tank (PLD that I know of anyway).
3) 270 accessories ain't gonna fly in Omega Savage. I think 1 at the very most, but by then it will have relatively diminished DPS value too once ilvls are 340 and accessory secondary stats start getting much bigger.
Whille it's true that indeed other party members have many tools to help tanks mitigate damage, the majority of these, we alread had and/or are rebranded into role actions. Only a select few (Passage of Arms, Intervention, The Blackest Knight, for example) are actually new, so I'm not actually of the opinion that on its own, it will make the difference. But you are right, it's speculation on my part, which I did imply anyway.
I'm still not expecting SE to role-lock anything pre-Stormblood because it seems to me it is as intended.
Also, instead of actually role-locking the accessories, they could do away with the possibility of changing equipment once you enter an instance. Tough luck if you get a dungeon drop while leveling, though.
Melding tenacity is pointless. And what is worse, they say it's not broken