The thing is with Lei shen was that in the first weeks you had no gear for it , afterwards there was the cloack from the quest and blizzard introduced the upgrades for gear and so while the boss remained the same in mechanics by giving those upgrades to players made the fight a lot more forgiving and easy . Garrosh didn't get nerfed like this and because it can't be roflstomped by gear like lei shen now it seems to be a lot harder. Depending on how far they got WoD blizz will nerf that fight soon enough i suppose.