Markdown is _fine_? I certainly have my own issues with it; most of which can be mitigated by adhering to a style guide (e.g. only use one syntax for <em> and <strong> as well as <ul> and headers). I'm not sure why we need both asterisks and underscores to represent the __same semantics__ – to me this feels wasteful of precious ASCII. Perhaps it was to allow the writer to express their preference while providing a shared and consistent meaning (same with the other duplicate forms). In that sense it seems to have done an <del>excellent</del> okay job at affirming common ground. I'm not sure. From what I can tell, the original author has been reluctant to do the work here and has left this for others (i.e. CommonMark).
I do love writing in Markdown, but my reasons are adjacent in some ways. It's a flat file, the syntax is easy to on-board new users with, adoption is widespread, and the HTML escape hatch is available. I only adhere to the syntax because I can usually expect a parser to exist for whatever environment I'm in.
I don't think this is the best we can do (or have done). I find myself conflicted about where to go next. Gemtext is nice! Except, what I often want is more expressiveness and consistency. This will probably be, for me, a spec that can still be run through a "reasonable" Markdown parser. When the output breaks, it still comes out as readable plain text (albeit with some weird ASCII scattered through my prose).