The concept is fine. The author may not want to manually write markdown, and may think that no one else wants to either, but they are wrong. It's very very useful to have a way to store formatted text without the horrors of full blown HTML. You can stick some markdown in a CMS database, render it on a webpage, and get the most common formatting: links, bullet points, bold. Great.
On the actual spec/implementation: yes, it's a complete disaster. Especially the way it is kind of mapped on to HTML, so you get weird things like writing "1. blah; \ 1. blah" makes a numbered list with a 1 and a 2.
But mixed in there, the author seems to have some weird assumptions that people are using Markdown primarily to write documentation, and this is somehow Markdown's fault. I genuinely don't understand this, or their point 13 "It’s 2022, we shouldn’t be using ascii-text to write documents."
Clearly we do need something like Markdown, but the existing attempts (including Mediawiki's "wikitext") all reveal that design a markdown syntax looks easy, but is actually extremely difficult to do well.