> Just recently I spent an hour unbundling a mail chain with layers of poor quote - reply - ask for clarification - further reply.

I'm not saying email is perfect or always works well, it just seems to naturally work better more often in some ways.

> The way we use slack is start a top level topic and group all related discussion in a thread.

My company has not been disciplined about that, and even when threads are used new ones get started to continue the same topic relatively frequently.