I don't think I ever see any Medium content linked to anywhere else outside of HN. Am I just missing some other sources? Is it a case of Medium writers link to other Medium writers?
You seem to be living behind a pretty good bullshit filter. Be grateful!
Unfortunately, I see a ton of mostly low-quality Medium.com links on my Pocket app's "Discover" feed. You can't block domains on that app, you can only flag links as spam, not of interest, etc. Flagging them doesn't seem to reduce the frequency of such posts appearing on the feed however.
You've probably seen Toward Data Science around a lot if you're in that field, which is based off of the Medium platform.