This can be said for any other team chat platform, as this was something I've always been wondering.
Alerts overload or too many messages during off hours? Under the same Notifications section as above, there's a Do not disturb area where you can set quiet hours. If it's just an app providing notifications of actions and such, you can select the channel and hit on the gear icon to the left of the search bar and mute that particular channel.
The default brush and knocking notification sound was pretty neat at the start then it just got obnoxious if people didn't mute their computers at the office. Head to Notifications > Sound & appearance under preferences to adjust this setting!
Requiring multiple accounts for multiple workplaces is kind of an hassle especially if you do a lot of collaboration. It's a design limitation and there's no solution for this unfortunately. 😞
Circling back to the original question of this article... No, it's not. For me at least but can't say for others, and this is just on a usability standpoint. At the end of the day, you don't need Slack to do work. If you're on there, it doesn't mean you're actually working.
It also seems that some companies also want an offering with a on-premise option as well, which Slack doesn't currently offer. They do have Enterprise Grid but that still seems to be cloud based. So for that, there's Mattermost by Gitlab which is worth taking a look at.
UPDATE: The recent update for Android (Oct. 10) appears to change how notifications work natively with your OS version and all of them seem to vibrate despite the setting turned off in app specific notifications (at least on Oreo). Looking back (according to their tweet in 2014 - https://twitter.com/slackhq/status/498544028569600000), it seems that sound and vibration have always been linked. While preserving the "Urgent" importance, so you still get pop ups, I've made sure the sound is set to "Silent" and "Vibrate" is toggled off. This seems to do the trick and stops your phone from rattling like mad if it's on a table!