I came to the same conclusion while trying to work out a good documentation single-sourcing setup that could successfully target multiple formats like markdown,

I came to the same conclusion while trying to work out a good documentation single-sourcing setup that could successfully target multiple formats like markdown, mdoc, be injected into code, etc. I still use markdown for what it does well, but I feel like virtually every other (lightweight) markup language misses the mark as well. Last year I started writing some posts that are about this in a very vague way (6 so far at https://t-ravis.com/room/doc/ https://t-ravis.com/room/doc/) to help order my own thinking and lay some groundwork for eventually demonstrating where a lot of them fall short. (Caveat: I'm not suggesting anyone stop using them for any given project that doesn't need to target multiple output formats. They aren't unusable. They just all have problems that make virtually all of them difficult to use as a single source.)