Last year I made $484.00 on Medium and $4.15 on Substack. In general the writing is better on Substack. Either the writing is better or you can more easily shield yourself from crap there. Apparently if you are a hotshot you can do well there. Paul Krugman, Joyce Carol Oats, Nadia Bolz-Weber.
Medium: the platform users love to hate. Contrast this with Substack. Everybody on Substack is prepared to defend it to the death and if that means offering up their first-born, so be it.
Don't believe me? I tried to get Substack to fix the "Open in App" button on the mountain of emails it generates. It sends you to Google play. (It works perfectly on Medium generated emails.) I logged help tickets until I was blue in the face.
I was on Simon Haisell's War and Peace slow read chat. He mentioned a couple of techs by name regarding some other problem some of his readers were having, that is, "I'll ask so-and-so and so-and-so." I described the link problem figuring he might could open a door or two, but I had people telling me I was a whiny baby for expecting software developers to write code that works.