I like to use medium mostly because of the insane reach it has, not because of the editing tools or the look and feel. My current workflow is to write the post on my blog (so that I own the domain and the source of truth) and then syndicate the content to other platforms like Medium, Dev.to or Hashnode.
I value the "you own the content" approach, and that's why I want to own my own content. I use jekyll/gatsby + github pages. It supports markdown, is pretty accessible to most developers, and other than the custom domain, it's free. How do you see this model compared to what the Hashnode developer blogs offer?
I think there's viability in a blog platform for developers, both from an audience as well as from the tooling (e.g. writing code snippets in medium is a PITA). But I'd be particularly concerned with the long-term viability of your blog platform. If you don't plan to have a paywall nor ads, how are you going to ensure your users that it will be around for the next 10 years?