Honestly the most effective tool I ever used to navigate a "conversational space" was trn, which, solely with the keyboard, you could follow threads (as a tree) and truncate uninteresting ones, block idiots, search, etc. All later ones have been slower and more irritating.
As a vim user that would be lovely. A short lived dream of a keyboard-centric discord has been killed by their ToS - third party clients are not allowed. Email is clunky, but it's decentralised and I can choose my client!
There was no way for example to do what the back button in a browser does without instituting a search through an unbounded number of messages and IIRC finicky use of the arrow keys during the search while consulting the "tree view" in the upper right corner of the screen. Doing the analog of the back button was easy only when the current message is a reply to the message you want to get back to.
Trn was optimized for the speed at which the user could consume (textual) information, but worse than the web at allowing the user to hone in on the one or two pieces of information (text) that the user most wants to know (even assuming a hypothetical world in which search engines do not exist).
Most people find learning new things and new points of view to be pleasurable (and the fast the new things and new points of view are consumed, the greater the pleasure), and I am no exception, but my experience has been that using the internet to chase that pleasure for its own sake does more harm than good. Trn was better at producing the pleasure than the web was because information could be kept coming at a higher rate than by using the web for the same amount of mental effort.
For example, when a person is done reading a web page there is some mental effort in deciding which page to go to next, e.g., which link to click. Yes, trn has keystrokes that say, "I'm done with this message, show me the next one" and "I'm done with this subtree, show me the next one", but I found it tempting to keep hitting the space bar, which yielded an experience in me of being constantly presented with new information ("stimuli") without having to make any decision or do any significant mental work, much like watching TV yields.
I am going to guess that unlike me, you do not worry about adverse effects from your spending time on the internet taking in a constant stream of information rapidly presented; am I correct about that?
But that's because trn was a "threaded news reader" not a "USENET archive search console". It was a very good tool for its intended purpose which, as you mention, was to consume a flow of news. Compare it to an email client or to other real-time chat fora. Also, it was a medium meant for participation, not just passive consumption. The client helped you find current topics and reply.
Generally, nobody expected a newsgroup message archive to exist much less for searching of stale messages to be a normal activity. The client tools and most servers were meant to buffer just a useful fringe of traffic to allow people to follow the flow while engaging and disengaging from the groups in async bursts. We would sit at the terminal and participate for a session, then walk away.
Back in the heyday of trn and USENET in general, it would be considered odd for people to hoard old messages, necropost on old threads (other than if there was some running in-joke to perpetuate in a certain group), or to be constantly online and obsessively responding with low latency throughout the whole day. Reply chains would often have multi-hour to multi-day latency, and higher volume groups were usually from more concurrent users and threads rather than more rapid messaging in a single chain.
Yes, same for slrn and (for mailing lists) mutt. It only went down from there in terms of effectiveness (PHP web forums, Reddit, Twitter, Discord, also HN).
Honestly the most effective tool I ever used to navigate a "conversational space" was trn, which, solely with the keyboard, you could follow threads (as a tree) and truncate uninteresting ones, block idiots, search, etc. All later ones have been slower and more irritating.