Slack encourages quick, stream-of-consciousness, short responses. Plus, it's hard to find past discussion, and it's hard to jump in after being gone for a few days (or, even a few hours).
Threads are absolutely the answer. But, the defaults matter - Slack isn't encouraging threaded, long-form messages. Instead, it makes all messages feel urgent - and it makes the cost of sending a message way too cheap.
I'm on a mission to bring back forums, where threading is the default. Inspired by YC's Bookface software, I'm working on a project to make forums as slick as Slack or Notion [1]. I think that long-form discussions and slow notifications are the key to bringing sanity back to discussions. And, I think the key is one amazing email summary per day - and few (if any) other notifications.
If you're interested in this problem - please reach out!