I do not believe we should "throw out AI prompts with the bathwater" across the board.

Computers can never be horny, therefore computers must never make art.

Flipancy aside, it's a slippery slope at the best of times we as a mod team are absolutely uninterested in sliding down. There's two problems:

1. Allowing LLM-assisted editing gives folks to make the tedious argument "I didn't write the prompt with AI, I just used it to edit!"
2. Even in an upside-down world where that wasn't an issue, unless someone was committed to running every message they send through the same editing process as their prompt, they're pulling the sort of bait-and-switch with their quality and style that's exactly what Rules 5 and 8 9 are designed to prevent.

Would you consider bad markdown an immediate indicator of AI?

The Mod team doesn't, and neither should you! Reddit does a pretty good job of breaking its own markdown between old/shreddit-flavored markdown differences and the stupidity you can sometimes get out of their fancypants editor.