> Basically, to get anything done you have to create channels, which is great for "top down, I know ahead of time what I need / want to enforce" structure, but awful for "this started as a one-on-one and is now a massive discussion with 17 people"

In Slack, you can turn a group DM into a private channel and keep the history.

https://slack.com/help/articles/217555437-Convert-a-group-di...