In general, I think people who say a champion is "broken" are wrong, because I think a champion can maintain their kit and still be balanced. Tahm kench, for instance, is overtuned right now because he can outduel too many top laners, but there's nothing conceptually wrong with his kit, at least in my opinion. However, I think morde is different. This is because so long as he maintains his gameplay identity as a juggernaut with his current ultimate, he becomes simply too hard to beat, even conceptually. The point of a juggernaut is that they can beat you to death if you stand next to them, but have a harder time getting close to you - Riot could nerf morde's numbers to the point where he couldn't beat other melee's in straight 1v1s, but I think he would no longer be a juggernaut in that case. When you combine this dueling potential which is usually gated by being hard to capitalize upon with morde's ult, which literally forces a duel with an enemy champion (including a ranged one, who would usually be able to kite you)... what do you do?