It wont be OP but it will help survival rogue. None said that will be applied with longer range. I'm also mage and rogue, counting that my main is tank. And rogues definitely need at least 25% damage reduction. Also it will make huge damage loss cause you'll be able only to use 2 and not 3 attack skills. We talk here about upgrade mastery to 25% instead 10%. And not stacking them both.