This entire thread has basically gone full circle and settled on the same old argument that my gigantic reddit/forum post from a month ago was talking about - http://forum.square-enix.com/ffxiv/t...eta-feels-off-.
The OP is technically right - parry is the only stat that affects our mitigation, and if the focus of a tank is to mitigate as much as possible, shouldnt we be stacking it as priority? The same argument is true to a degree with Vitality vs Strength - if we're there to not die, then surely stacking the "don't die as much" stat is the favored option.
There's no disputing that a level 60 Tank who has stacked parry on every single item, wears full fending, and stays in Shield Oath/Defiance etc will be easier to heal than one who avoids all parry and stacks Crit/Det, wears full slaying and tries to stancedance into DPS stance as often as possible. Of course the first tank is easier to heal.
The question though is the -degree- in which it is easier... and it's not much. The way the game works, you just don't have constant incoming damage or spike damage of the magnitude where the parry/vit/shield tank's overall toughness makes any real difference to the success of a group. However, the strength/crit/det/sword tank will be pushing 30-40% more DPS than the turtley tank... and in -most- cases nowadays, that extra dps is just far far more useful.
No one is FORCING tanks to avoid parry or focus dps 100%, but the hard encounters the game currently has basically -suggest- it, and groups where a tank cannot contribute a meaningful amount of dps simply have much more trouble clearing it. There's no disputing that Parry/Vit makes a tank easier to heal, the fact of the matter is that it just DOESNT REALLY MATTER with the content we have given how dependant everything is on proper cooldown rotations.
By all means play the parry stacking "brick wall" tank, and in 4man dungeons and content where DPS checks arent especially important then the success of a group wont really be affected - heck, if your healer is undergeared or new then it might actually improve the chance of success. But for any meaningful difficult content tanks simply cannot ignore the fact that the benefits gained from Parry are virtually nothing, but the benefits gained from increasing the damage output can have meaningful improvement on group success when it comes to pushing phases, skipping mechanics, and hitting hard enrage timers.
Just because DPS do -more- damage than tanks, doesnt mean that tank damage isnt worth maxing too. And until the tanks that are advocating parry/turtle/defensive style tanking over a style that tries to prioritise damage output truly realise just how important to success tank DPS can be, it's unlikely that the dps-is-important crowd will be able to change their mind.
What it will take is a wipe on Living Liquid due to not hitting the hand-split DPS check by half a percent, or a wipe on Thordan because the bladedancing knights didn't die fast enough.