Which, of course, is only one person's experience amongst many, and different people will have different experiences.
For people like me, however, the problems listed in this article are painfully obvious, especially with regard to false sense of urgency. When everything is urgent, nothing is urgent, except my heart rate.
Slack isn't really the issue here: it's any form of synchronous communication (IRC, someone coming to your desk, getting a phone call). Slack just happens to be the latest flagship for the interruption armada, swooping in with their false urgency and lack of sufficient information.