Earlier quoted context omitted.
No its not. What I find frustrating about Slack is that it gives certain people the ability to say "i didn't see that" regarding important work information. I regard properly reading your email part of your job, and if you're missing important emails, you're failing at it. I find that unless you send an email alongside whatever Slack notification, many people will just ignore it.
The problem with Slack-alikes is that you get buried under a deluge of notifications, so it is needlessly difficult to stay on top of things. Email is far better in this regard.
Now, if someone sends me an email, it might get buried between other stuff