I already think that markdown is barely ok for writing documentation, and the experience of plugins in mdBook is why I tell people not to use it (edit: it = mdBook). The base flavor of mdBook is minimalistic. Maybe that’s a good thing, that you’re given a minimalistic markdown as a starting point? But if it’s minimalistic, then it’s certainly missing some things that I’d want to use in the documentation I write, and the experience of using plugins is, well, not very good.

My current recommendations are MkDocs (material theme), Jekyll, and Docusaurus. Hugo gets a qualified recommendation, and I only recommend mdBook for people who are doing Rust stuff.