I agree with all the asspats for dang on the day-to-day moderation level. If anything I'd like to see more of a heavy hand from him. I've modded some moderately-sized Reddit subs and it was hell.
However, in strategic terms, I think HN has failed to maintain a good comment signal-to-noise ratio over the past several years. For instance it used to be that "funny" or entertaining type of low-effort comments would be strongly discouraged with downvotes; at some point in the past few years it has become very common and... REminiscent of another social site that I'm not supposed to draw comparisons to due to HN guidelines.* Now it's common to see jokes and puns do quite well.
Fundamentally, to maintain a board's culture you need to encourage people to "lurk more" to get acclimated to the board's culture before participating. In other words you need to throttle/retard new users' participation somewhat.
I do recall at one point a push to increase commenting by removing comment average karma in user profiles. (Some) people used to withhold commenting unless they felt they had a real banger because it would throw off their ratio. It also used to be new user signups were only open occasionally rather than always available.
My hypothesis on where it went wrong is cost-free upvotes. Downvotes have always been gated behind a karma threshold, but any new account can upvote whatever it wants. Floods of new accounts thoughtlessly upvoting the types of comments they upvote on other sites will easily outpace the old timers' downvotes on that same content. Over time, this small change in karma dynamics shifts the board culture.
* Like the guideline wording, dang frequently brushes away this critique out of hand, but as someone who goes long periods between visiting HN regularly, it's very obvious to me. I think you could quantify it if you took random samples of HN comments from various time slices and noted the quantity of low-effort comments.