Spot on that promoting one’s work is primarily one’s own business, but the essence of any platform’s value proposition is that publishing there helps, in some way, improve your content’s visibility.
Serendipitous discovery does seem to work nice and natural on Medium … but when you actually go hunting for content, that’s another matter. Possibly I’m too old school, but I can’t help thinking that the single way Medium could help it’s writers find their audience is to make it easier for the audience to find the writers.