Super interesting, I didn't know it was a reaction. Looking at Usenet thread screenshots, I think the UX issue with their threads is that they actually listed the title, not the actual message in a branch format. Whereas Reddit has the actual message content in a branch format.
I think the flat sequential thread works fine with a limited number of messages.
Eventually with enough replies it degrades to being very unwieldy like traditional forums.
In fact here's a screenshot from 2005
https://www.flickr.com/photos/third/18260796