Yeah, I'm well aware that markdown didn't happen in a vacuum and was inspired by plain text formatting conventions. But there is only that much you can cover in an already too long blog post. It wouldn't have changed my argument much either. It wouldn't be historically accurate to say that Markdown existed before Gruber/Swartz, like it wouldn't be accurate to say that HTML existed before Tim-Berners Lee, even though SGML and such was a thing.
I'm not arguing for a more proprietary binary word processor format either. Or that we should type JSON. It's actually possible to have decent WYSIWYG editors that does their job. And they won't get better if don't put our minds to them.
The point you're missing in this reply is the legitime user-unfriendly experience of markdown and the challenges it poses for developers who are trying to solve things for their teams and customers today.