The real problem with Reddit is that even small subreddits tend towards beginner or introductory content because that reflects the level of understanding of most users.
Having separable, more focused forums can allow for discussions at a much higher level of knowledge and expertise than Reddit. You can see plenty of examples of this today with HN having better content and discussion in its niche than anywhere on Reddit, and plenty of complicated high-skill-ceiling discussion topics like vehicle maintenance or travel hacks still being discussed at high quality on oldschool forums.
I don’t see a benefit for Usenet because it wasn’t obsoleted by Reddit, it was made obsolete by forums. Honestly I just wish those would make a resurgence. They allow for so much more customization than Reddit, Usenet, or Facebook and don’t have centralized policies constantly messing with them. And I really don’t think there is a need for a one-stop-shop site or tech stack for focused discussion. Reddit and FB may have replaced forums in most cases for most people from 2010 to now, but as they’ve become more commercialized with more rules, maybe we can switch back