P2P does not scale. Nostr is not P2P. It is distributed. Distributed systems scale by their nature. The more people use it, the more relays pop up.
An essential part of this is the low friction to set up relays, and the fact that relays are not a form of lock in - this is where we beat federation models.
As relays get too heavy and performance suffers, people simply migrate to faster relays.
The fact someone corps easily run a public relay on a raspberry pi ought to say everything.