How can I actually escape OTP hell?

Im a Mordekaiser OTP for years now at 300 LP with 2.1+ million points on him. The problem is I am really bad with other champs. I tried forcing myself onto Riven and Qiyana (mostly this 2) top for around 50 games each to build a real champion pool, but Im still really bad with them past the laning phase. In mid and late game im really bad with other champs even in plat games while im master with other champs and I have around 40% winrate in draft with them.

Has anyone actually gotten out of this kind of OTP hole? Any advice appreciated.