There's nothing stopping you using slack for thoughtful drawn our discussions. My experience is that in slack the people who send quickfire messages are the people who send quickfire emails, and the people who send thought emails send thought our slack messages.
The big advantage of slack (to me) is that people use channels, and it avoids the "I mailed X and Z, but forgot to CC y in on this", where people routinely selectively email people when really more people should be aware.
The big advantage of slack (to me) is that people use channels, and it avoids the "I mailed X and Z, but forgot to CC y in on this", where people routinely selectively email people when really more people should be aware.