Your view is that email is better than slack. OP has experience with email and judges slack to be better. Neither are “right” or “wrong”
I find Slack is better than Skype For IM. I find zoom the best for face to face meetings and screen sharing (slack doesn’t seem to have a “share this window” option), but slack for starting a quick call and for asynchronous comms, and things like changes and alerts. Email for comms outside the company.
The fact that OP has used email doesn't mean that he's done work collaboration exclusively over email. Obviously some of the people who have done both might prefer Slack, but the difference is so large that I find it unlikely.
I find Slack is better than Skype For IM. I find zoom the best for face to face meetings and screen sharing (slack doesn’t seem to have a “share this window” option), but slack for starting a quick call and for asynchronous comms, and things like changes and alerts. Email for comms outside the company.
Use whatever tool makes you work well.