I'd challenge this.
IMHO, Slack is pretty decent if one instills 3 rules in corporate culture.
#1 - No DMs. Talk about all work in an open channel. Radical transparency will also make you a better company.
#2 - Keep replies on the same topic in threads. I.e. don't use it like IRC. Conversely, don't put unrelated replies in a thread.
#3 - Post-back end solutions/resolutions. A thread should NEVER end with "I'll DM you" or "Let's talk about this offline"
If these are followed, at some point you reach critical mass, where "question someone wants to ask you" is discoverable in your history.