We generally define “compatible” as “meets consensus in Babelmark”, e.g. the unavoidable diverging implementations of Markdown (as the spec was ambiguous-by-design) agree most on this set. See for yourself.
But you’re trying to redefine what Markdown is (which I think is why John Gruber keeps getting upset). Markdown has a spec which CommonMark unambiguously violates. I happen to agree with your changes, but they’re not just “Markdown without ambiguity”.