The core argument against Medium is: "Until you host your content on your platform, they will always live at the mercy of the company hosting the platform."
But unless you own a datacentre, you are always using someone else's platform, whether it is a cloud provider, a colocation or anything in between.
If my domain registrar, my DNS provider, my hosting company, ... go "bad" I can just move and my readers won't notice. Even if you are on hosted wordpress etc, you can archive your site as is and move, preserving the URLs. That's not the case with Medium etc where your content lives under their domain.