They'd be just as fast with Slack or whatever, for the most part.
EDIT: as someone posted below:
> The open-ness of code, visibility, diffs. It was perfection. Something broke in my env suddenly? OH, I just checked recently pushed diffs that affect my realm. Hey there it is, security pushed something weird. I'll just revert the part that affects me and tag them. No meeting, maybe a SEV for visibility and review, maybe not. Easy peasy.
This is the kind of empowerment developers are given and expected to handle (both the explicitly ability to revert previously committed code and the implicit responsibility that the teams code that was overridden must deal with it once they're notified rather than push back)