Interesting perspective! I've tended to think that the majority of people who join Medium are there as writers, with reading being secondary. You're working on the basis that there are lots of readers with little interest in writing. That's not what I see on my feed, but then if they're not commenting, perhaps they're essentially invisible.

It may be that my writing does attract other writers, while top writers do attract more people who are just here to read what those top writers push out. If that's the case, they will be bringing in reader revenues. But I'd argue that a lot of the people following the top writers are also writers interested in replicating what they do, so they can succeed too.