Honestly Mordekaiser is a whole mess of problems, not the least of which is that he has garbage bast stats, on the other hand I understand why: his Iron Man passive sort of acts to counteract his lackluster base stats in theory. The problem is that, short of you facing an idiot that doesn't understand Mordekaiser's kit aka the new champion effect, in a practical scenario Mordekaiser will never be able to engage on a person without busting a summoner or some sort of item effect because he has no ability to engage beyond lumbering slowly towards an opponent, or hope someone ELSE can engage for him and he can try sprinting to catch up.
So Mordekaiser's passive is only as effective as Mordekaiser being able to use his abilities on a person, and without cc or mobility Mordekaiser basically has to answer instead of question the enemy laner. Literally, Mordekaiser's only hope is that he can push the wave so hard that he forces jungler attention, manage to survive being ganked, and keep his opponent from roaming... this is only really effective in the mid lane on assassins who often have horrible wave clear and want to roam and have trouble killing Mordekaiser in any case.
In top lane, all Mordekaiser can do is push like crazy and hope he can take tower despite the top laner, since many top laners can force a fight on their terms, or just dial a jungler to gank or mid to roam for a virtually free kill; his prominence in the mid lane prior to his rework was literally because he couldn't function in the top lane where he was originally intended. And in the bot lane, Mordekaiser is wholly dependent on his support to start a fight because he has the weaknesses of top lane exacerbated with the fact it's a 2v2, so he often needs the right support with more cc than someone honestly should bother having, such as Leona or Nautilus.
Honestly the only solution I can pitch is to make it so Mordekaiser doesn't need crowd control or mobility to win 1v1 even when he is always made to be engaged on, and survive into the mid and/or late game, and with the way the game is right now, the only feasible means of doing that is making Mordekaiser so monstrously tanky and damage-y that not even duelists like Trundle, Fiora, Xin or Jax or random champion #444 want to 1v1 him without the stars aligning. It's certainly not a good solution, it'd be better if Mordekaiser could simply answer an opponent better because he is almost certainly the one to be engaged on - and not the other way around - when a fight starts.