I find Markdown attractive for writing on the computer. The guy has good points.
Part of the attraction is that developers have been trying to use markdown to create nice gui's for writing, like zettlr. It's very satisfying to see all the colors and headings change by putting the pound or asterisk symbol, etc.
It's nice that a lot of people have latched on to the format, and we all feel we can use these text files to get around in life. I think part of this guy's comments doesn't appreciate the aesthetics of the writing community.
But again, on a technical level, he has points...and I have struggled very much with the conversion of documents.
I think he's writing out of long experience and frustration.
And he's right in that markdown was devised for techies - programmers and web writers of the day. Thats why code blocks have a degree of precedence. And it doesn't have many features, like colour, that some writers use: random acceptance of different HTML is frustrating. As is random acceptance of bits from other languages like YAML. It's like a bicycle invented by a carpenter, the idea is good but it's stuffed with issues that many feel they can solve with a bit of bodging; and competing carpenters conventions which decide which bodges should be used more widely.
And all the previews and wysiwygs depend on a conversion to HTML, which conversion is inconsistent, as he points out.
Most of the time it doesn't matter to me. I'm usually quite happy with text. But it depends what I'm doing. I'm used to using multi colour highlighting when I'm editing or reviewing, but colour use is reserved for syntax in a text editor (otherwise they'd compete). I'm used to sophisticated tables in some areas of writing; there are some fairly easy primitive editors, like Typora, but generally much easier to produce tables in a word processor.