Some interesting points, but Slack is what you make of it. I have found it to be a great resource for working on remote teams. Sure, there is a tendency to be on 24/7, because of FOMO alone, but like Twitter, or other online tools, is what you make of it.
The key is to keep perspective and not lose your humanity. Perhaps it helps when some team members have bigger issues to deal with, such as a newborn child, or a husband with brain cancer. This applied to two of my teams, and helped keep a lid on the time spent on Slack.