But that's the thing, it's not Quality over Quantity.
PLD has more mitigation tools than any other tank, but they're all more limited, half don't effect you, and some consume job gauge.
GNB has Heart of Light, one skill, blanket mitigation on yourself and the whole party.
In it's place, PLD has Divine Veil and Passage of Arms, one is an awkward cone AoE that requires channelling and doesn't stack with Sheltron, the other requires an additional GCD cast to activate and doesn't even effect you.
Nothing about that says "Quality over Quantity".
It's a bit more mitigation sure, but the way it's implemented is definitely Quantity over Quality.