Moreover, the parent comment linked to a decent PR presumably human made. If an LLM had written the PR, its description would be 9 paragraphs long and the code changes full of assinine comments.

If the author really did one-shot the PR, then the author must have also put in the extremely detailed and tedious work which would be required to tame LLM output for this specific repo, in which case, they actually put in real effort, applyed expertise and thoughtfulness, which is the whole issue at hand.

You think coding agents or models have not improved in 3 years? From my experience they absolutely have. I've spent a lot of time getting Claude Code to write clean features in a brownfield repo. I've gone from it helping me speed up to now Fable 5.1 doing it perfectly. And there are steps one can take to improve the quality which is to teach it (SKILLs) your important design and coding standards, as well as automatic design or code review to catch edge cases, performance issues, or whatever aspect you find a high priority.