Well, Substack is Substack and Medium is Medium. Medium actually doesn't want to compete, just be who they are. Each company has their own funding model and each targets different users. I have people giving out on Reddit for posting tech articles behind the paywall because the expect everything for free. It's tough making this all work at the right price while making sure writers also make a decent amount.

I again think it's better to have the audio on another platform as you could essentially diversify your income stream. The one thing where Medium could help is you pointing it to a source of your own audio hosted somewhere else and then it would play that as the default option the the button is pressed, but that could piss off Speechify, the company that Medium pays for this service.