"Anyone can start a server" is only true when you're lying about what a "server" is. (Or redefining it to the point of usefulness.)

A Discord "server" is just a defined chat namespace. All the Discord chat "servers" live together on the same actual load-balanced VMs or whatever on the physical servers they run.

It's honestly the thing that's annoyed me most about Discord from the very beginning, long before they introduced the ads and the microtransactions and the mandatory doxxing.