>And telling maintainers how to act will not fix anything.

Indeed. For too long, maintainers were expected to be gracious, courteous, and polite at all costs lest they be labeled "problematic", except for a few who were too influential to be muzzled like Theo de Raadt or Linus.

Perhaps we need to normalize bullying people who submit obvious slop as PRs.

No, you absolutely should be gracious, courteous, and polite. But only at first. The duty of maintaining a functional community doesn't mean you're obligated to suffer unlimited abuse.