My email use is very different. What actually lands in my inbox is person to person communications (some of it is commercial, like from my accountant or salespeople I reached out to, but it still comes from a person). On a busy day I might get a handful of emails at best landing in the inbox so email is not a problem for me.

I make sure to unsubscribe from any newsletters as the first step after signing up for an account so I don't receive any, and automated notifications I can't opt-out of are filtered away.

The big problem you raise about "spam" (whether real spam or unwanted newsletters) are a problem with defective privacy legislation that allows companies to get away with it as opposed to problems with email itself. If marketing communications were made opt-in by law (one that's actually enforced) this will dramatically cut down on the noise in people's inboxes.

Commercial correspondence regarding an ongoing deal (like the examples you mention) seem like a good thing. I want my landlord or bank or other suppliers to be able to contact me if they want to as long as it's not marketing (which would be addressed by the previous point).

The problems with non-technical people having their inbox flooded and constantly saying at 10k+ unread emails is because they fail or can't be bothered to manage it (by setting up rules and unsubscribing whenever possible). I don't think it's a flaw of email itself.

Privacy is the only thing here I agree with, and I believe that can be solved with public keys embedded in the DNS (itself protected by DNSSEC). The problem with that is lack of mainstream client support (whether for S/MIME or GPG); the protocols email is based on don't seem like a blocker in this case.