I think it's a decent argument to the extent that I can't really think of a counter-argument.
One anecdotal thing is how I recently came across a whole other type of user (non-bitcoiner or non-obvious) by searching relays instead of discovering users via my follows.
I also think that a "killer app" would push nostr on other communities that are looking for a place. This is where I agree with John about the hackathon mentality, but also understand this because there is really no incentive (minus jack and opensats funding) or corporate structure. I digress...