> There are systems in place to prevent fast back-and-forth arguments.

Like what? I never saw anything to suggest that is the case.

> Not having a mentions functionality for those who wish to use it doesn't seem to to change anything around over-heated discussions.

Of course it does. If you have to keep checking manually, eventually you’ll get distracted. By the time you come back, if you do, there may already be another reply to the reply and you may no longer feel the need to comment. Nor will you be inclined to respond to a comment made days later in a nested discussion, because you won’t find it. But people just arriving at the thread might, and continue the discussion with new perspectives.

> I'd make @ a page like 'threads' which just includes any comments with @$username.

To each their own, I’m thankful HN doesn’t have that feature.