Can't speak to the data sci Medium content, but Medium's low barrier to entry is its downfall for programming content; I will ignore any Medium link I see because the articles are somehow nearly always crap. I suspect most programming articles on Medium are just devs employing that advice re. getting hired, i.e. "get your name out there! Start a blog!"
Towards Data Science. They reached out to me with some kind of profit-sharing offer after I wrote something on Medium a while back. But I have way too much interactive content on my personal site that wouldn't translate to Medium, and I don't do it for money anyways.
It's actually a decent platform. Some people write weird stuff on it but at least they're trying an alternative to ads. In my opinion, that puts them above every ad-powered website out there.
Logging in is actually really easy. It's by email and doesn't use a password. Also, Medium uses subscriptions rather than ads to fund itself. I would rather have a popup or two than a shitty ad-infested website.