You just described three link aggregators, sites whose purpose is to spread third party content. The audience is the people posting Medium articles, and the people who follow them back to Medium.
If the responses on their site to articles posted there are any indicator they don't even have a built-in audience any more. Even articles that make it to the front page here, the hn comments are half or more people complaining (rightly so imho) about medium.
Medium used to be good, people published good content there. but as they increased their gatekeeping it seemed like there was a sharp decline in quality and quantity.
I'm not disagreeing, but it doesn't really matter how high the quality of the content is on any site, more people on HN are going to complain about the presence of javascript and attempts at monetization than will ever bother to read the article.
It only happens more often with Medium because Medium articles are posted more often. I don't think it's an objective indicator of much, beyond HN's generally cantankerous attitude towards the modern web.
