I will give you that solo lane Morde needs some help to be viable, but other than that, what's wrong with Morde?
And if you're one of those people who says he "doesn't feel like Morde", why do you feel this way? I honestly think he still very much feels like Morde, but I see many people saying otherwise.
It isn't; it's just different from the established meta.
Him being in a solo lane is actually worse for the game because of his complete lack of CC or mobility preventing him from being able to set up ganks and making him awful late game because he is taking the place of a champion that ordinarily is providing CC for the team, and his shields making the lane a complete stomp one way or the other almost every time.
In the bot lane, he isn't taking the place of someone that would otherwise be providing utility/CC or dive potential, and a support with CC can set up for ganks in his place, or keep the enemies close to him so he can get his damage off.
See Bot lane Mordekaiser for why.
Also the fact that he can make a 6v4 or 7v4 now, has always been ridiculous.
The problem is clear: a champion needs to be so overloaded and broken in order to be played bot lane against an ADC/support that it's completely garbage in terms of game balance. This is what Mordekaiser is teaching us.
The few games (like, 3?) I have played with Mordekaiser have always felt terrible just because I remember back when I was Pre-30 how Independent I felt with Mordekaiser. Sure, he had problems, like a lack of mobility, but 335 movement speed wasn't Nightmarish. with Boots and Movement Quints, you could still make up for it. it didn't feel as bad because you had a lot of base damage and a lot of innate power. It they caught you out 3v1 you could turn right the hell around and bash their faces in, you could siphon them, you could use Creeping Death on yourself to give yourself tank stats and deal even more damage.
Now he feels like a Bitch. His Movement Speed, even with Quints is TERRIBLE, His W literally doesn't exist without an Ally Champion in range. His Q requires them to be stupid and stay in your range and is split between three attacks instead of one massive bash to the head. Yes, he has more damage and better scaling, no one is arguing about that, but for that scaling we now have a champion that cannot function independently. Everyone Else in the game (except 
) still has Full Access to their Abilities if they get caught out and can turn around and die fighting. Mordekaiser just can't do that anymore. He's no longer the 3v1 Champion he used to be. He's gone from Low-Elo Hypercarry with good counterplay to the High-Elo Burster that requires an entire team built around him.
Essentially 
turned from 
into AD 
. Mordekaiser used to be able to Solo Carry, now he requires an entire team built around him to do anything.
Feast or famine. Polarized gameplay. Defeated at champ select(enemy counterpick). Low counterplay.
These are problems Mordekaiser had pre 5.16 his winrate was 51% though so close to balance despite these issues.
Current morde problems.
Feast or Famine x10.
More Polarized Gameplay.
Still defeated at champ select ( if not by enemy,then by your own supports choice)
High counterplay.
Problems that needed to be solved to make him a healthy champion were made worse
This is the core of it
Just a bunch of ADC mains butthurt that he's occupying their role and actually doing well against them in lane.
