While yes they had cosmetics in the game before, it was added in Legion, when nobody was changing weapons, so it didn't matter if people were getting them off the loot table. With this being off the loot table, it means people who can use it are getting weapons loads faster than they should be, which is problematic for balance and unfair for those that can't get it. This is the first time they ahve had cosmetic weapons with a separate loot table in the game when changing weapons was viable.