There are different kinds of clients. One kind connects to a community relay (or more than one) and operates like IRC, and hears people only on those relays. The other kind (my kind) operates like a web browser, and if a webpage references a resource at a web server, it goes and gets it, without the user having to setup a list of approved webservers from which to fetch resources.

Gossip has write relays - that is where you post and I think users *should* manage them. Gossip doesn't have "read" relays. It finds people and events wherever they are, and uses a lot of things to do this (but not randomness) including kind2, kind3, kind10001, nip05, nip23, p and e tag hints, previous success with that pubkey at that relay, and also relay statistics (number of successes versus number of failues, hangups, etc).