From my (limited) experience of writing a documentation page for a library I made, Markdown is pretty limited (speaking of CommonMark here). Even basic things like table or image need HTML to be done. The gain in syntax is lost on the coherence side as the document mixes two languages, and an additional step of processing the document is required to transform it in full HTML.
It have it use cases but writing long and complex documents is not one of them.
Some other, non-standard variants of Markdown also handle tables via a syntax which resembles ASCII art. And while that format does do an excellent job of adhering to Markdown's ethos of remaining readable in plain text; I usually prefer to use HTML fallback anyway as it's easier to maintain.
The most commonly used Markdown variants (Github, So, Reddit, probably Slack) support tables, they've been in use for years and work well. I can't believe Commonmark can't just standardise what's already being used by the majority of users.
Some of the suggestions in the discussion thread[0] don't pay any attention to this, and if they agree on something that nobody uses it'll just be ignored.
It have it use cases but writing long and complex documents is not one of them.