This is inciteful.
I'm not convinced that there are many people who come here just to read. But if there is, this helps explain a few things:
1) I doubt that my material is leading to new subscribers. If the Medium algorithms are able to pick up on this, they might be relegating me to a lower frequency on the feeds.
2) This explains the top writers. Their topics are a good first impression and may turn a lurker into a subscriber. Hence the preference in the feeds. The top writer finds the formula for Medium success--and is able to convert more lurkers to subscribers. That's a good positive feedback loop and explains why top writers write about the same thing in the same way over and over. But many original fans tire of these writers. Hopefully they find the more unique writers.
So there is some evidence of more readers than writers.
However, I think most of us who put articles on Medium have an ulterior agenda; i.e. somehow earn a writing income. Unless I am extremely slow, most articles require several hours of effort. This is far different than other internet forums I have been involved with.
I came to Medium as G+ was shutting down. Medium was recommended in several G+ I belonged to. I quickly saw a higher degree of intellect on Medium and subscribed immediately. So I did not see the frustrations as a lurker.
Having said, the Medium feed is a mystery to me. I would say 30% of my feed is from writers I have chosen to follow. 10% are top writers who I do not follow. 60% are also unfollowed writers, but the algorithm does a good job of selecting articles within my preferred reading choices.
And there are writers I have followed yet do not show up on my feed.