Pre LLMs I would have said the all-text format of HN probably kept the astroturfing low, but these days I'm less sure. It's still a much less engaging format than almost any other place on the web, although again, with LLMs you can even cheaply target the lowest value returns.
Reddit is an all text (or mostly all text) community, and it is heavily astroturfed in many subreddits. It doesn't stop the astroturfing.
You could read obvious shilling here pretending to like or pay and use the boringest B2B SaaS products way back too.
Trying to get a proper grasp of consensus on open forums is hopeless.