I do not think that is the problem with markdown lol. There are lots of problems with markdown, especially vanilla or the more limited versions of it - but really its super power is that it is readable with a regular text editor (or `cat`) and can be rendered without a compilation step.

Markdown is not competing with latex or typst, it is competing with (and has won against) .txt files

There have been theoretically precise published specs for serious markdowns for 15 years. The commonmark convention is a common specification for many including e.g the familiar simple github variant, which emphatically does have a completely perfect specification.

As I said in a previous comment typst especialy with extending via scripting stops being plain text readable. A Markdown file (whatever flavor it may be) is still fundamentaly one vi,nano, Editor, Notepad++ away from being read with all its context included. It is a tradeoff that for READMES I would not want to make.

Of course it's extensible, you can put HTML in it, and HTML is extensible.