The 'distraction' thing is one I keep seeing about Slack and I often wonder is this because individuals just are not managing notifications properly (or at all) or is it FOMO that causes the individual to habitually check channels?
There is no proper management of notifications. Either you store them completely out of sight (and thus are not notifications, but messages), or they interrupt you without taking into account how important the work you're doing is.
I hate notifications, and is why any time I've been forced to use slack, I use it through their irc gateway and disable all notifications.