Slack is still better for sending out random links and messages about lost car keys or whatever, rather than having those clog everyone's inboxes, but beyond that it quickly becomes an anti-pattern that enables a huge array of self-destructive behaviors.
"Slack is heroin" is pretty accurate. Instant communication (and video games, and Facebook, and Y-Combinator ...) feeds the gratification / pleasure parts of the brain. That's great if one is working on their own time and can enjoy the inevitable crash when everyone else has finally gone to sleep, but when you've got a company full of people flitting around like crazy, because their neurochemistry says they have to "keep up", because "keeping up" is what keeps the brain in a happy mood -- that's a bad thing.
Changing collaboration software won't do a damned thing until teams have a chance to attend Narcotics Anonymous meetings.
Slack is heroin (is the point), it is great to start, and seems great for a while, but for many people it gets worse and worse as time goes by.
You have not answered the point at all.
Obviously many people spend their lives enjoying heroin (with no bad affects)
But for many it's toxic, why are you not just an addict selling something you yet don't understand?