I run a publication on Medium, Better Humans. My understanding is that the pivot to be a place where most writing is paid for was specifically to crowd out content marketing. The content marketing is, as the two of you say, basically Wikipedia summaries and people selling themselves. It's part of the style guide for their Membership program that writers can't have calls to action (with a few exceptions, like if it's an excerpt from your book).
It's been a great program for us. We write in the area of personal development and it's allowed us to pour a lot of money into getting authors who've actually tested their advice and then working with them to write very thorough tutorials that other people could follow.
In my biased opinion, what we used to compete with was trash simply because it didn't work. Content marketers were writing great headlines for productivity advice they'd never tested, the advice had huge gaps or mistakes, and then it would stop short of telling you what to do so that it could make some call-to-action sales pitch.
We've been getting much less competition for page views from these trash articles based on recent Medium changes. The biggest change was that they manually review all articles before allowing an article to get promoted by their algorithm.
As an example, I have an article I wrote that's just creeping up on 1M page views. That just wasn't possible before.