It would be highly illogical that SE would only add a hidden modifier on a single job out of the 9 jobs in the game, and only DEX when it comes to parry rate. You can't make any sort of statement from the data he's posted so far because the sample size isn't nearly big enough. The margin of error is too wide to make any significant guesses as to how much it's affecting the parry rate. There are also other factors that could be involved. The limited parry rate testing that was posted from Valk-Dancing mad lacked information on whether they tested just parry w/o a shield on the PLD. From what I understand the test was done for Shield Blocks specifically but because they had the data they included parries as well. We don't know the priority of Parry vs Shield. Maybe both PLD and WAR gain the same boost from DEX for parry but because Shield Blocks are checked first you won't see as many parries on a PLD.
For the record, I'm not saying OP is wrong or that his test is pointless. I'm saying if he really believes this as a possibility he needs to do extensive testing before posting any results. Wide-eyed enthusiasm after a few short trials only helps to spread misinformation about whatever it is we're missing about WAR. Frankly I'm convinced the "more research" comment was a backhanded way of saying "We don't know what's wrong either so you guys figure it out". I would rather keep my hopes low and be proven wrong than keep my hopes up only to have them come crashing down.
