I think his shield/true damage is very strong, but I don't think he's broken. He's a juggernaut - he's supposed to be able to tank a lot of damage and deal a lot of damage if he gets near you. He does both of those things well, the same way Darius, Garen, and Mordekaiser do. He's easily kited, the same way all juggernauts are. His W shield/damage scales up as he takes damage, but decays immediately very quickly when he doesn't take damage, so if you hold your next auto for half a second he loses most of his damage and safety. I'm not saying this is ideal, but it isn't much different than buying a QSS and just cleansing Morde's ult every time he uses it, or buying a zhonyas so Zed's ult is useless - except holding your damage for a second costs significantly less gold.
Do I believe that he single-handedly beat your team? Yep.
But only because I've seen games where an Ashe jungle singe-handedly carried my team. Any champion can get fed, or the player can play it very well, and they can basically 1v5 .
Just to clarify, I do think he could use some nerfs. But when a champion has such clearly defined strengths and weaknesses, I cannot, in good conscious, say they are "broken".