I completely agree. It is also the effort to interruption ratio that has reached a tipping point. Once upon a time if I wanted someone's help right now i would have to walk to the actual desk, and bribe them with caffeine or chocolate. If the effort of levering myself out of my chair was greater than the benefit to me I stayed put - hence interrupting another person had a minimum price point - the other person may not like it but the price was paid in public and there was a perceived value to the business.

Phones reduced that price point - but it still has a cost to me.

Now IM / Slack has flipped it on its head - the cost to the interruptor is negligible but the cost for the interruptee is their mental derailment - and no ability to judge the overall benefit of helping until it is too late

Plus I don't really see the win - for real time co-ordination it's hard to beat a mass phone conference ( we are doing a complex release with phased rollouts and devops watching the traffic - then get your headsets on, and everyone must hurry up and wait)

Slack is just secondary for that - useful for spelling out what has been said but otherwise ...

For letting others know what has happened - that's called an after the fact report or "email".

So really i don't see the use case except it means that when like the phone, i reach you i am confident of a reply in a given time period - that may well be defining facto