You realize PLD can parry too, right? Block vs. Parry isn't an either or thing, WAR get parry, PLD get block + parry. They could gear for parry if they felt like it.
Either way, lets just say you ignore the additional baseline mitigation afforded by block. Enhanced Convalescence + Shield Oath (sorry, not Holy Shield) blows Convalescence + wrath + mantra out of the water. It's over 50% more effective and you don't even have to bother with wrath stacks or slotting and using 2 cross class abilities.
This is also ignoring rage of halone which makes Convalescence even MORE effective against STR based enemies.
