I see. I kinda agree with you on a big part, but I still think full commoditization is both impossible and undesirable.
The reply spam stuff is just one example where relays are required to do something.
Imagine Nostr isn't this messy half-assed relay-based thing, but instead it's a perfect p2p system where everybody is always online and easily reachable. There are no relays. I imagine this is close to a system you would like to have, ideally.
In that system spam is free and everybody has to run powerful and imperfect antispam systems that filter a neverending stream of spam.
Now in the current world in which people run Nostr on their phones that becomes even more unfeasible. It gets worse when you realize that relays have to be chosen to be read from, and, worse, relays have limits -- so if you ask for the last 500 events you might get 500 spam events, and even if you filter all of them locally you still only got those, and you've missed all the important events you actually wanted to read.
Does that make sense? Do you see my point?