I've heard you say this on a number of threads and I'm kinda curious what makes you think this way. From limited numbers between me and my friend, PLD's parry+block rate seems to equal WAR's parry rate, at least to the degree that they're comparable. Just glancing over something I got from running brayflox HM: as PLD I was getting around 8% parry and 17% block, give or take RNG, while I heard from my raid tank doing some parry testing that he was getting around 25% parry rate. From this I'm assuming blocks are calculated before parry, and since you can't parry and block at the same time PLD's get a significantly lower parry rate.
Maybe I'm missing something really obvious here, but I don't really see how PLD's block provides any kind of advantage over WAR's parry.