Unfortunately HN is likely astroturfed just as much as any other forum, despite the otherwise seemingly substantiveness of HN compared to sites like Reddit. And unfortunately there's no way to cancel out bad faith flagging and downvoting the same way you can reply to bad faith commenting. It's more invisible and easier to abuse (once the karma thresholds have been reached, which isn't hard).

The mitigation mechanism is moderators like dang who manually intervene

It's not perfect, but it ain't nothing