So here's my big question about Mordekaiser

If the champion wasn't really capable of functioning in the botlane without the XP passive, why did he get one in the first place?

I understand that Riot wanted him to be able to play in that lane, but shouldn't a champion's place in the meta be determined by the playerbase and the champion's individual merits? For example, Quinn and Valor were intended to be botlane marksmen, but function almost more effectively mid or top. That's the playerbase looking at their unique strengths and weaknesses and finding a better role for them to play. Mordekaiser however goes entirely against this. He gained an unfair advantage over duo lanes thanks to a tacked-on passive that only exists because he couldn't duo lane.

If Mordekaiser was incapable of duoing without the passive, he shouldn't be expected to see play in that role and certainly shouldn't be shoehorned into it. Instead, focus could have been given to his sololane performance (which Riot did a good job on in all honesty).