Is it meant to be? The appeal of Markdown is that it's easy to remember, reasonably friendly to non-technical people, and it looks good as plain text.
If you write a plain text document and you format it following markdown principles, you get a simple rich text version of your document for free. Your headings will be headings, your bullet points will be bullet points, and your code blocks will be code blocks.
Now, you can also ‘game’ markdown, writing the minimum possible plaintext to ‘trick’ it into making a pretty document while leaving the plain text ugly.
But in general, the idea of markdown is to start from ‘imagine I have a bunch of plain text files I’ve been formatting consistently for years. How can I make them look nice as rich text?’
I'll note this tension has a long history in CS: https://en.wikipedia.org/wiki/Worse_is_better
And I think it has a lot to do with a very particular notion of good, which is something like "conceptually pleasing to someone who has mastered the space".
If you are solely an English writer then yes. Using md with some languages will quickly turn you into its hater. Certain formatting symbols aren’t easily accessible in some layouts, like backticks for code or ^ for superscript. Some symbols require extra keystrokes like ~ in german. Some layouts will require finger yoga exercises. Basically, any other text markups based on English (including LaTeX) are unfriendly to other languages. Thus an abnormal popularity of md across the apps makes them much less friendly for non-English users. Mobile typing pushes this pain to another level.
For a while, when I originally switched away from my native language QWERTY variant, I would sometimes need æ ø å on the computer and I would Google aelig oslash and aring respectively and find the symbols for those letters that way :p
Just look at some of these other examples the author lauds. I've been writing code for most of my life and I find roff's manpage to be absolutely inscrutable. I don't understand the context in which you'd need to pick between roff and Markdown, they seem like they're solving completely different problems for totally different audiences.
Yet, I had to crank out diagrams recently, and found every single program I knew had become enshittified to the point of not being usable.
I got the job done with asciiflow box-and-arrow diagrams, pasted into a word processing document as monospaced-font paragraphs.