I think of simplicity as the ease of reading and writing and less so parsing. Sure there are many ways to parse markdown, but regardless of which one you choose it's easy to engage with.

This post/example/thing completely misses the point of Markdown. Yes it's clever in stringing together edge cases to try to claim it can identify specific parsers. But it's also pointless.

Markdown is for writers.

Markdown was designed up front to mimic common conventions in text-based communication, particularly email.

It was designed to be easy enough to read and edit as plain text, while also being easy to convert into basic HTML.

It was primarily designed for prose.

It always supported an escape to bare HTML where direct handling of how things are represented is needed.

It's not a programming language. It's not an object encoding language. I see no expectation that two different parsers would deterministically return the same thing when the language is based on common convention with a lot of flexibility built in, rather than a strict specification.

In my opinion it has gained widespread adoption well beyond it's original design as a parser for blogging precisely because it's imprecise.