On the other hand, there's no gatekeeping on custom domains, right?
I have a custom Medium domain from back in the day when you could get them, and it doesn't suffer from any of the usability problems and dark patterns of the actual medium.com (though I should probably move away from it anyway).
So... it's a "dark pattern" to give you access to some articles for free and then, should you like them and want to read more, ask you to pay for them?
Dark patterns are tricks, like making you click on something that you thought did one thing but does something else. Asking you to sign in/up is hardly a dark pattern.
And I've yet to see Medium "fill the screen" with annoying banners. In fact, from what I've just seen, Medium just displayed a web page with the article's bottom half telling you you've read all of your free articles and asking you to sign up.