When I was working on onion routing and mesh networking 10+ years ago, I remember reading a paper that showed that in a mesh network every additional node added total throughput capacity, but the rate of increase asymptotically approached 0.

I don't have the citation handy, and I'm sure the proof was tied to a particular topology, but the take home for me was that it was possible for mesh network advocates and skeptics to both be correct; that mesh networks can be a way to continually increase network capacity cooperatively without centralized authority, but that doesn't mean such capacity increases would be meaningful.

The same might apply here: yes, the rate of increase in N may approach 0 such that at some point it becomes an irrelevant factor to economic growth. OTOH, in the absence of alternative drivers even a tiny rate of increase is something, and removing it could lead to accelerating reductions in global wealth.

But we just don't know. The relevant questions and answers are more empirical than theoretical. My point was just that the growth narrative isn't predicated on a pyramid scheme, it's just the safest and possibly only known reliable strategy we understand. But an end to population growth seems inevitable in the next couple of generations (barring space colonization), so I suppose we'll find some answers rather soon.