I was also disappointed by this overly simplistic and cheerful view.

Async communication, like most things, isn't equally well-suited to all scenarios (never mind people).

I worked in a primarily async environment and while I, as an individual, like many aspects of this manner of work it is sometimes a terribly inefficient way to get things done. In some instances a meeting with a handful of people can save you weeks of back and forth on Slack, each time with a bunch of context switching.

Please read again, it doesn't work for everyone. The TLDR from our own experience is that it's hard to make it work for juniors.