Your mistake is showing a channel list. Hide unread channels; it's the only way to use Slack IMO.
I've been on this site since 2007, I've been around the block a few times ;)
Channels may exist for each corporate customer, of which there may be a hundred or more, where CS reps subscribe to subsets that they're focused on, country managers subscribe to those that are local, product managers subscribe broadly by vertical but only scan to get a feel, sales may subscribe by function or region, etc. This is an easy way to get a large number of useful channels that simultaneously cuts down on noise.
BTW, you're surprisingly dictatorial in what you say. Emergent behaviour is far more interesting to me, because - along with conscious reflection - it evolves uses that can't easily be foreseen. Where did you get your rules handed down from on high, how were they justified, and what right do you have to think they are correct?
Sorry, you're right. Nothing is set in stone, all rules have their exceptions, etc.
My point was that having too many channels can lead to a constant sense of urgency, FOMO, and increased anxiety. If you have a carefully defined way of using them, without a sense of urgency, and without a need to see everything, it may work.