PLD has two forms of perpetual damage mitigation. First is the -10% STR debuff from Rage of Halone and second is the fact that you can equip a shield. Blocking will mitigate significantly more than parrying for any physical attack (so you know...almost everything Twintania does to you). Since PLD has the same parry rate as WAR, this is pure extra mitigation that a WAR does not get. Furthermore, you can blind a lot of things in t5 (I've never tried, but I strongly suspect you can't blind Twin...), so you effectively have increased evasion almost half the time if you time your Flashing correctly.
For the record (and because I cut it out of the quote) I don't need Tempered Will for Divebombs either, but it's nice that you can use it if you want.Seems like mileage differs, for T2 Enrage, there is no reason not to solo-tank with a WAR when they output higher DPS, almost all the LS groups i Know of switches to WAR for T2 Enrage tanking. [snip] Spirits Within, I'm not sure why you're having the tank do the silencing but if thats your setup then yeah. [snip] Cover, well, barely used and barely useful.
WAR doing higher DPS is (largely) a myth. The tanking stance penalty for WAR is 5% more than the tanking stance penalty for PLD to make up for things like Unchained. I remember seeing somebody somewhere suggesting a WAR in Defiance could do like 10-20 DPS more than a PLD in Shield Oath if they really tried, but that both were too pathetically low to be worth consideration. I don't think these people even took into consideration Shield Swipe which is a DPS increase for PLD (though, obviously, not available in t2).
Personally I've always gone with PLD for t2. There's the fact that you can escalate your cooldowns without holes if you get stacks of the debuff where a WAR cannot, can use HG to reset the stacks to 0 if the healers aren't keeping up, can just wait for all your cooldowns between every encounter since you're waiting for enrage anyway, and the fact that I almost always do the silencing in alternation with a Bard since Spirits Within is off GCD. SCH or MNK can do it too, but often they would rather not so I just do it.
Cover+Hallowed Ground is a really great skill on p6 of t4. Everything (except maybe the rook, I don't know since a DPS always gets it) does pDPS there and you can just let the WHM gather all the mobs in the room to the middle for you to pick up without any worry at all. You can also use Cover on the other tank in some encounters to circumvent some mechanics or save them from a bad healer (sometimes it just doesn't matter at all if OT dies and matters a LOT if MT dies)