In my opinion, it buries the actual discussion on the post in question under a stream of name-mentions.
Imagine if people on HN didn't email an article link to someone, but just @mentioned their name as a comment. With a ranking system like HN's, established comments would rise, but there would still be a ton of crud making it harder to, say, see new comments.
I think you're right and it just demonstrates a lack of good intuitive UX around content sharing. Instagram is especially bad in this regard, popular posts are just polluted with @ mentions.
Imagine if people on HN didn't email an article link to someone, but just @mentioned their name as a comment. With a ranking system like HN's, established comments would rise, but there would still be a ton of crud making it harder to, say, see new comments.