So what is PLD good at?

[Reynhart]

In a purely hypothetical situation, which would literally never happen, where both tanks stood infront of the mob, somehow held agro and yet did absolutely nothing... Yes, Shield Oath is slightly better than Defiance.

I think it's more of a hunch than real effectiveness. The purely hypothetical situation is enough to make healers uncomfortable and seeing bigger damage on the tank is scarier for them.

But likewise, I'm struggling to think of any scenario in the game in which pld is better than war as an off tank.

There really isn't one. Defiance being off the GCD combined with how much damage a WAR can do just makes it the ideal OT.

According to calculation, if the WAR put the slashing debuff, an equally gear PLD in SwOath will always do more damage than a WAR without Defiance. Not a "lot" more, but more nonetheless