Interestingly, as an early users of the software, I got mostly the exact opposite feeling.
Build it for a real community and try to make it work within that community
Ember used Discourse for the past several months. We provided a ton of feedback and I like to think that our participation served exactly this purpose: building Discourse for a real community.
Make it possible to close threads, write summary for threads, group threads together, explore a topic
I'm not sure how much of this comes across in the pitch, but these specific goals are focuses of the software. For example, Discourse supports a "Best of Thread" view (see https://github.com/discourse/core/blob/master/app/models/pos... and https://github.com/discourse/core/blob/master/lib/score_calc...), which is currently only triggered on a very high threshold. I like this feature a lot. You could easily imagine it being possible for moderators to hand-curate the "Best of" view in the future.
There is also an "aggregated links" view that aggregates all of the outbound links from a thread and shows how many times they have been clicked on.
Discourse has moderator tools for "closing" threads. I would expect that closed threads would work well together with the "Best of" view.
Bring more structure than linear comments, but less complexity than threaded comments.
I think this is one of the team's highest priorities. There is some innovation in the way replies work, but it's also possible to "reply as a new thread", with margin links between the threads. I have found this to be a very good compromise, and something that explicitly attempts to tackle your desire here.
In short, I think there's more depth here than you're seeing at first glance, and the things you want to see from Discourse are things the team is actively thinking about.