I'm not one to complain much....but seriously Tahm Kench is out of hand

Ok, so how the hell can you consider tahm kench remotely balanced. Had graves, ziggs, poppy (me) all ult on him, and he still killed me in no time, got another kill i believe, and walked away. We were hammering him with everything we had for a good 8-10 seconds, and that is with me stunning him. He only had armor. Another time, we had all 5 on our team going at him under base turret, 3 ults again and he just walked away. His whole team could sit back and pretty much just wait it due to the amount of damage he was dealing and because his stacks would build so fast, that he would just grab us and throw into them. How can this amount of damage be allowed on a champ that builds no damage items, plus with his slow and stack that last forever.