I can't see any mention here, but does Medium pay their authors for the content? Or is the pertinent question, how well does it pay compared to other article sites?
Medium does not pay a majority of their authors, however, I've heard that they pay some "big names" to help them gain traffic.
So unless you are a well known blogger/journalist, don't expect a check.
So sites like Medium are effectively driving down the pay of most authors (except some stars) by competing with other sites that pay for content. Bad news for authors.