Docs help, but they don't save you from a team that treats Slack as the source of truth. At 50 people the bigger failure is ownership: nobody knows which page is current, nobody gets time to fix stale docs after the process changes, and after a few rounds of that the wiki becomes a museum piece new hires learn to ignore.
Configure Slack to only retain messages for a month or so. People will stop relying on it for such.
Can’t you do that by not paying?
That’s a culture/leadership problem.
Slack is communication, not documentation.
It should be, but I’ve also seen few teams having everything on slack. Better ones at least pinned stuff