Ironically, the only use I have for Slack is to communicate with an external web developer that we contracted.

In my world... EVERYONE (50/50 internal and external) is on email and/or Teams (or the phone). It works. Shit gets done. It's a small, high-trust environment of autonomous people doing rapidly changing work.

There is a working world where email makes sense and trying to "make Slack a thing" would be (rightfully) scoffed at. If I'm yanked out of this and dropped into some Slack/ticket/KPI/whatever environment I will adapt and play ball.