Email communication, slow, initiator feels ignored. Slack/chat communication, instant, receiver feels overwhelmed. The problem is not email or slack, it's the method in which we communicate. We need to make sure we use the right tools, as the author mentioned, knowledge bases, email, chat etc at the appropriate times. The problem is not Slack per say, it's using Slack for all communications.
If someone does an @here or @channel or even an @person notify for a simple question that is not urgent, that is rude. Non-urgent issues should go in the channels and the person can respond when they get time, or e-mail it to indicate it's not a priority.
I really like Slack, but I do agree that it's easy to get carried away with notifications and integrations and it becomes a lot of noise. But most of these issues can be resolved by talking as a team about how the tools should be used.