Tell me you have never used roff without saying you have never used roff.
After using it for 25 or so applications, I got the feeling that having markdown as the "source of truth" was slightly easier for reading, editing, and diffing different versions. I’ve been using it with Markdown as a base and I’m happy with the results.
To me, Markdown wins on ergonomics: easier to visually scan, no escaping of typographical marks (the `\-` hyphen), and syntax highlighting in every editor for bold/italics/etc,
I do concede that raw `roff`'s tend to produce better "one-per-line" diffing on what would otherwise be inlined paragraphs. But that seems somewhat minor to me.
Also, I invite more advanced `roff` users to show me the error on my ways regarding my above reasoning.