> HN does something similar (…), new comments get some seconds/minutes on the top of the comments

Only kind of. There’s some time/upvotes algorithm that determines that. If a submission has been live for a few hours or a day and already has a number of highly upvoted comments, new ones can appear so far down the list they’ll realistically not get read. Also, some submissions simply don’t get engagement, it not rare to find some with one or two comments, read by effectively no one.