I have written on Medium for five years and Substack for 2 1/2 years. I agree with much of this but my experience is slightly different.
After the 90% Medium paycut couple of years back, my earning on Medium went from $100-$200 per month to $5-$10 per month (writing humor and fiction. The non-money makers of writing.) With 2.5k followers.
On Substack I have 11 paid followers (without any paywall. They just want to support my writing.) Earning roughly $400 per year ($35 per month.) So I am earning more on Substack with 11 paid subscribers than I do on Medium with 2.5k "followers." I am not getting rich either way.
The first year I was on Substack, there was no discovery built-in. The promotional burden fell on me and I only reached 400 subscribers (10 paid.) But this past year I went from 400 to 1032 (11 paid) subscribers with zero promotion on my part. Substack is working hard to up newsletter discoverability and it is working. Most of my new followers come from the Substack network now.
I get far more comments and likes on Substack now than I ever did on Medium. People who subscribe want to read your writing (for the most part.) There isn't the "follow to get followers" nonsense that plagues Medium.
I rarely read Medium any more. I have found so little worth reading the past couple of years (only a couple of old timers who are still around) and you have to wade through so much "throw something up every day" writing to find it.
With Substack newsletters, you only get the good stuff from newsletters you want to read. And the reading app makes it so convenient.
And I used to love Medium during the 2018-2019 era. But I will probably drop Medium after my year runs out (I just renewed. Not sure why...) I simply enjoy reading and writing on Substack so much more.
At least until the next great writing thing comes along. And I take my writing there. 🤓