But turning off notifications is not using the tool right. The fact that you have to turn off notifications indicates that most people use it incorrectly (e.g., @channel/@here-ing for super unimportant messages).

Slack does a really poor job of guiding its users to use the tool properly. There is no warning when someone decides to @here the #announcements channel with 200+ people to wish someone a happy birthday. That's poor design.