Early on in conversations about the design of email, anti spam techniques such as having each send incur a cost was, suggested.

This was rebuffed and lead to the surveilance capitalist distopia we see today.

Nostr is resistant to this by virtue of its early integration of V4V. Zaps. I

It's an "easy" horizontal leap to paid or subsidized relays (that offer non-abusive advertising schemes).

It's another "easy" horizontal leap to I tegrate non-btc zaps (such as Monero)

Another interesting Question to ask is: is NOSTR more resistant to the type of protocol attack suffered on XMPP. 
SMTP kind of blew up with the popularity of the internet and was only one of many competing standards. 

Nostr's, like XMPP is more "elemental".Its simplicity taps into "fundamental particle" level of design. 



 

 XMPP was also killed by big tech. But your other point about zaps seems sound, but I've the feeling it isn't enough.