Mordekaiser has too much counterplay and will likely only be a pubstomp champ
The new Mordekaiser has shockingly little agency in his lane now; his early trading is horrendous, moving up to mediocre if he gets to hit an isolated Q, but more importantly, he can't fight at all unless the enemy lets him. He has nothing to assist in landing his E, the opponent has to basically let themselves get hit by it unless they have long cast times, and he has no means of keeping the opponent in range to get the damage off unless they handshake him and agree to the duel. This isn't even mentioning how for such a melee centric champion he's quite horrible at dueling other fighters. In addition to that he is very unsafe in lane and has little to deter jungle ganks. He's also horrible at fighting ranged champions who have constant harass.
This wouldn't be too bad if he were a scaling champion but he's still mostly a mid game oriented fighter. He gets hard outscaled by other carries and all of which except for Kayle usually have better means of keeping themselves alive. And Kayle runs Klepto to make up for that weakness.
I guess it mostly comes down to how strong his R turns out to be in higher ELO, and given that its so easy to escape I am a bit concerned, but from what I've seen and played Mordekaiser really isn't that threatening against people who know What they're doing. I can understand why LS said he has a weak kit; its simply too easy to counterplay him.