I think when the main stream magazines like The Atlantic, New York Times, The Economist, etc. left, a lot of readers left. I also think that many well established writers left then. They were poached, I think, by Substack (who offered them 4 or 5 figures).

Ev Williams changed this to a 'wannabe writer's' platform because he lost readers, and writers outnumber readers by about 5 to 1. So the greater market is for people who want to learn to write.

I truly doubt that Medium has been successful in being step number 1 for a career as a writer. One can certainly make money out of offering courses, etc. but that doesn't make one a writer - just a marketer.