The single most frustrating thing for me about Discourse is when I’m catching up on a long thread, and I see a comment I want to reply to. So I quote the text and type my short reply.
Now Discourse jumps me to the bottom of the thread, and it’s incredibly frustrating to try to find my original place to continue reading. Combined with the flat nature of the discussions, this highly disincentives me from participating in long threads. Mailing lists are better at this.