The latest HN comment dump I could find with a quick search was from May 2018 [1].
There were 237,646 comments in total that month, made by 36,358 unique users. 75% of users posted 5 or fewer comments, with a median of 2. The most prolific user wrote 798 comments, dang managed 6th place with 425 comments.
Even if the numbers doubled since then, there is no need to moderate millions of users, as only (well) tens of thousands of them are actively participating.
[1] https://www.reddit.com/r/datasets/comments/6v685o/complete_h...