Braydon Fuller on Nostr: Right, however in my case, I noticed the relay was either a paid relay that we happen ...

Right, however in my case, I noticed the relay was either a paid relay that we happen to share (single point of failure) or a wot relay that uses someone elses pubkey (not including my contacts, even if I'm in theirs) and will probably only store notes temporarily.

Yes that is part of it. With many different clients; short notes, git collaboration, long notes, video, audio, markets (desktop or mobile) and etc. (desktop or mobile), it could get quite complex for each separately to do all the heavy lifting of communicating with thousands of relays, etc. etc.