what to use as Ring 2 as War?

[Leiron]

I don't see that your support for the statement "more health is always better for tanking" has anything to do with that statement. You have not justified why you would want 450 HP over superior mitigation.

You are suggesting that parry, which is chance based, is at all comparable to true mitigation i.e. shield oath.
It really is not comparable due to the nature of parry.

Parry in itself is not constant, so the actual mitigation will be less than what one would expect.
At best with a 20% chance of parrying an attack and mitigation 25% of the attack, you're creating a mitigation of 15%.
That's a best case scenario.
It also cannot be controlled, you cannot determine when you'll parry a hood swing or a weak hit for 200.

If the boss hits for 1k over a period of 10 seconds and you parry twice, you mitigate the damage down to 850.
That looks good right?
But bosses don't hit for uniform.
What if the boss hits like this

10,10,10,10,10,10,10,10,10,910.
What if you parry two of the tens?
Well you go from 850, and instead move up to 996.
Now you only mitigated a mere .004%

Furthermore, Parry works ONLY on physical abilities.
Vitality works on both elemental AND physical abilities.

Stacking vitality absolutely affords absolute greater survivability, stacking dex does not.
It makes no sense to tell someone "Use a gryphonskin ring over a fending ring" then say in the next breath that "allocating for anything but vitality as a tank is wrong."
Attacks that typically kill a tank are hard hitting abilities that typically cannot be blocked/parried.
The bosses in Turn 2 do not use a single physical abilities, so your increase in parry does absolutely nothing.
Vitality also directly affects the mitigation of abilities such as Thrill of Battle, and also means your healers have a greater cushion to heal you when you take a hit.

It is also chance based.
If you are busy tanking Caduceus with a gryphon skin wing and say "well I MIGHT parry his hood swing and survive 1200 health" w but what if you don't?
If you don't, you die.
If you went with vitality you'd survive with 450, but your heals can top you off, or you can pop an IB afterwards or a second IB even if infuriate is up.

It is better to go with vitality over a dex, you cannot control parry, you cannot will parry into blocking the one physical hit that can kill you.