Still seems overkill. It's just headers, lists, block quotes, codeblocks, and a few inner emphasis and link formatters, basically. HTML is the whole jungle for a gorilla with a few bananas here.

More importantly all HTML is valid markdown.

That doesn’t track at all. Markdown was created as a simpler way to mark up text than HTML. They are both ways of encoding a document that provide ways to convey intention. HTML is no one’s end goal.