alt Hacker NewsBiggest problem of mdBook is the lack of the good PDF and ePub export[1]. This is why Quarto[2] (based on pandoc) is a better choice if you need both online and offline rendered documentation/text. And Typst (or LaTeX for more conservative folks) for the offline documentation/articles/books.
I get where you're coming from but I'm not sure if PDF generation was a goal for mdbook to begin with. I'm pretty sure they're working on it now, but I'd stick to a domain specific tool, personally I find typst excellent to generate documents for prints.
For simple HTML docs mdbook is also excellent. I don't know if you could combine these two domains into one tool nicely. To me they're just too different.
although I have made presentations with mdbook using custom written preprocessors and a custom renderer (all of which were extremely crude, but did the job)