Discussion about Mordekaiser

Despite him of being in the "Forgotten list of champions that will be eventually be reworked in future" He is pretty weird Champion, He is easiest to kite that's true, his solo lane isn't strong at all, he can't jungle well, he has lowest movement speed and his tank scaling stats are very bad compared to the rest of the Juggernauts class. In some situations i see him or i play him as insane monster who can 1 v 3 in Twisted tree line, or 1 v 5 in summoner rift, but i am still not sure if that's either because he is very well in late game or because he is specialized against some sort of champions, but the majority of matches Mordekaiser seems very useless everytime i play him Ap or ad, even if i build him Full tanks he still doesn't do something interesting beside only rylais/deadman plate are the good items on mordekaiser because he really needs to have a nice speed and slows people to start getting close to them, but rylais was nerfed long ago and Deadman plate isn't enough for his overall kite. What do you think is the secret of Mordekaiser? Why is he very weak most of the matches but he is insanely a godlike who can 1 v 5 in some sort of matches late game.