You can fetch notes just from 1 relay if you want on amethyst. Yes thats true the last part you siad.
Discussion
I know about that. I was wondering if there was a way to only see notes that were only published to one relay. Notes on one relay might exist on another.
I suppose there is no way to know if notes were only published/broadcast to a single relay, but you could eliminate notes from a feed if the client discovers them on more than one of the relays it's subscribed to.