That can work for some slacks and some channels. But with others, not so much. When you're being paid to pay attention to client needs, there's only so much you can get away with.
But Slack still creates the expectation of immediacy in a way that other tools don't. Handling the same number of clients via email is a whole different experience. And Slack makes it very hard for people to filter out noise.
To my mind, Slack is to virtual work what open offices are to physical collaboration. They can be used well, but the default is a continuous drain on attention.