Mordekaiser and Iron Man
Alright, I think the issue with what Riot thinks makes solo Morde unhealthy is good ol' Iron Man. It's an awesome passive and is one of the reasons Mordekaiser is among the best duelists in the League of Legends. But the problem is that it's unhealthy in that in benefits Mordekaiser when he is just chilling in a solo lane during the laning phase, with little pressure to do anything other than push and get the jungler's attention, just as much as it does when he tries to smash his opponent in the face in a duel.
In bot lane, there is so much going on down there that you have little to no time to rest, you have to be moving, trying to last hit and avoid being poked by the enemy laner, who can poke you readily and consistently in the laning phase without expending any sort of resource as an ADC.
Hence, Iron Man is considered 'healthy' in the bot lane, but in mid and top for the laning phase, it is considered oppressive to an unhealthy degree since you can just shield to ignore poke and win through thoughtless attrition, and a lot of those mid and top laners have to use mana to deal with you while you can chill and use your health, hence why he is considered unhealthy solo.
Beyond the laning phase, Mordekaiser's passive isn't an issue because everyone is roaming and starting to look for teamfights, where Morde's weaknesses are displayed in full detail, it's the laning phase that people have issues with for solo Kaiser at mid and top.
Before you suggest it, I doubt nerfing Mordekaiser's damage or whatever he has for utility would solve anything, it would just create more problems and create a giant seesaw of Mordekaiser being underpowered or overpowered with buffs and still wouldn't address the actual problem.
So what should we do, lower the base Iron Man cap at early levels? Make maintaining Iron Man consistently more relatively costly at early levels through increased early health costs? Make Iron Man drain rapidly outside of battle?
I'm not suggesting a flat nerf to Iron Man, it's not a problem beyond the laning phase, it is just considered oppressive during said phase when solo Kaiser goes mid/top, so reducing the power of it in the early game may be just what the doctor ordered for solo Mordekaiser to get a passing health check.
Maybe then he can get his solo W damage.