Medium is the next generation of magazine where the users are content creators instead of the publishers. You can post to medium and get the distribution benefits of a publisher that people know and look to for content. Not everyone wants or can spin up their own hosted blog and drive people to it at the same time. Many people want to focus on writing, not publishing, so they use something like medium or twitter.

I agree there should be other publishers, but the doom and gloom over medium is a bit strong. Any publisher, social network, or central repo suffers from the same complaints.