Agreed. I think in 2016 Slack just got absorbed in their own thing. Slack is pretty good and has some nice features but not really anything a big Acme corp can't copy. And I'd expect Slack to be another case where 90% of people just use direct & channel messaging, no or few apps, etc. which means the switching costs are very low.

Although on another side, MS Teams is still miles behind Slack. While you can be signed into multiple orgs in Teams, switching orgs literally restarts the program which means that switching from your org to a client's org is super disruptive. If you are in a video call your only option is to open teams in the browser to view another organization.