If everybody used the same 2 relays, yes. But if everybody chooses different 2 relays it's not centralizing. You don't need to "be on" a relay to read somebody's notes from it. You just need to connect and read, and you can stay connected if you want their future notes as they arrive, or you can come back later for more.
Discussion
Fair point. I only considered read&write connections to relays! But there are as you say the possibility of read-only connections as well. Then all that gets possible without tangling everyone up in the same two.
:) Best regards, and happy Sunday to you!