Can’t anyone already do that with a screenshot or a log dump? I’m always assuming company provided comms platforms are fully readable by the admins

That's a good operating assumption, and I usually think this way too.

It turns out Slack actually requires legal process or consent of parties to provide private messages to admins: https://slack.com/help/articles/204897248-Guide-to-Slack-imp...

But of course yes, another party could simply take a screenshot