In my opinion, the Parry stat is bad not so much because it's random but primarily because the stat just plain doesn't increase parry rate enougn, and even if it did, the parry mechanic is incredibly stupid in this game. Even the producer, Yoshida, admitted that the stat doesn't do enough but it would take too much fiddling with the numbers to fix it, so they'll look at it next expansion. Therefore, it's actually a good thing to avoid Parry. I know how stupid it sounds because it's a stat only for tanks, but I've accepted that the devs messed up, they've admitted to it, and it has to be treated as a dead stat.