There's the quality of the written commentary (which is all that matters for anyone only reading, never posting on HN) and the quality of the engagement of people that do write comments (which include how much their learned, the emotions they had, and other less tangible stuff)
I think HN is optimizing for the former quality aspects and not the latter. So in that sense, if you can't tell if it's written by a bot, does it matter? (cue Westworld https://www.youtube.com/watch?v=kaahx4hMxmw)