I have to disagree with this. Nothing distracts and annoys me more than watching the bouncing Skype typing indicator and thinking my coworker is deep diving into an important topic and after three minutes of typing all I get is "yeet!"
Skype IM does not scale at all. Slack can also be a problem with bad culture or the wrong channel breakdown and etiquette, but it at least offers viable tools/notification controls to tune it so you can have both social interaction as well as heads-down focused time.
