Bit of a side question to your main points - I'm curious how you factor certain fundamental differences between Medium and Substack into your possible move. Although Medium is sorely lacking healthy community, it is still a community-ish platform, where for one yearly fee I can read, and when moved comment on, a lot of different writers, some who stick around, some who come and go, some who bore me after a piece or two, some I read intermittently, some I read regularly. Substack on the other hand is a perfect reflection of our pathologically hyper-individualistic society. Each writer is in their own little personal echo chamber. I have to pay per person to read any given person, and nobody else can I read or comment on for that fistful of dollars. For readers such as myself who like a family-size sampler box of writers, variety and diversity in topics and styles and subjects, it sucks. It is anti-social and un-communal by design, isolating each writer and their readers and commentary.

So it seems to me it would be even worse than Medium, for a Penguin of the Argumentative sort. The only interaction you'd get would be from your specific subscribers. Nobody else could read you there, unless you write for free of course.