HN's model is bad for high volume. Sometimes on HN you only get one top level reply on the whole page because once it puts the top top-level reply it then puts all the replies to that above the next top-level reply.

So you get a vast amount of low quality replies above the next high-quality reply.

For low volume it works okay because you can manually collapse but for high volume once it starts paging it breaks down and you just get further into the top level comment without properly being able to escape.

Reddit's model of auto-collapsing so you get a mix of threads and top-level replies is much better for picking out the better responses.