Sion's broken kit

So a game with 4 assassins and two adc's both with over 15 kills and a full tank sion does more damage then everyone but a zed? Wtf is riot thinking with a kit that can out damage most people in the game simply by building tank. At level 9 sion can half life a fiora simply with a knock up and his shout when only having ninja tabby? Why is a champion whos entire purpose is to build pure tank have a kit that does more base damage with no stats then even supports?