PLD theorycraft?

[SeraviEdalborez]

Parry is not a worthwhile stat when "average mitigation" doesn't matter because "avarage damage taken" doesn't matter, base parry rate is already sufficient, and needing so much parry to give any return makes it not worth investing in.

As a tank, the only things that ever threaten your HP total are huge attacks like Mountain Buster, Death Sentence, Ravensbeak etc or a bunch of attacks from multiple enemies intended to be tanked separately (T7 Melusine+adds, T8 Avatar+Dread, T9 Boss+Ghost) or a big dungeon pull.

For these situations you never rely on your random mitigation (block or parry). You always pop an important cooldown like Rampart or Sentinel (or Inner Beast as WAR with some other cooldown additionally). Your healers cannot "underheal" in anticipation of a block or parry because you will die. Therefore when you parry or block you usually cause overhealing anyways. If you die from such a big hit due to not parrying or blocking it and you popped cooldowns, that's a fundamental problem that you and your healers must fix somehow by mitigating it better. Parry won't fix it.

Falling into the pitfall of "it's a mitigation stat, I'm a tank" is short-sighted.

[dramamine]

As a tank, the only things that ever threaten your HP total are huge attacks like Mountain Buster, Death Sentence, Ravensbeak etc or a bunch of attacks from multiple enemies intended to be tanked separately (T7 Melusine+adds, T8 Avatar+Dread, T9 Boss+Ghost) or a big dungeon pull.

Those things aren't really comparable. You're right that Parry doesn't really do anything for big single attacks, but parry's definitely worthwhile during a big dungeon pull or any time you're tanking multiple enemies, because that's where average damage dominates. That's also the sort of situation where extra DPS stats are the least worthwhile (at least as a PLD).

I think you're looking at it from the wrong direction. You don't stack parry because you're expecting a single parry to make the difference between life or death. You stack parry because the benefits of stacking DPS stats are extremely marginal for a tank in tanking stance, and parry decreases the amount of damage you take over time.

And a healer most certainly can underheal in anticipation of a block or parry. It's called staying in cleric stance and using abilities like stone skin, lustrate, benediction, regen, and so forth as the primary means to heal the tank rather than relying on cure/physick. If you take less damage over time, that becomes easier to do. Obviously they still need to top you off before big hits and that sort of thing, but it's not like there's zero benefit to increasing your mitigation over time as a tank.