This advice does appear to be coming from someone who writes webpages using roff... The core argument simply seems to be that markdown lacks sufficient structur

This advice does appear to be coming from someone who writes webpages using roff... The core argument simply seems to be that markdown lacks sufficient structure to build "documents," which I agree is absolutely true and essentially part of the design. IMO Markdown isn't intended to structure documents; it's intended to enhance plain text. If you find yourself constantly tweking at whitespace or special characters to provoke your markdown to behave, or if you are using so many features of md that you have to keep a reference handy, maybe you ought to use something different. As an aside, I have used Front Matter (essentially a YAML header on markdown) for cases when a bit of structure or metadata is needed alongside a blob of text, and I think it strikes a great balance between writability and structure. Markdown tables need to die in a fire though; what a wreck.