I see what you mean. I used to think that too. What client are you using ? For me on Amethyst, seeing and adding what relays you are posting to is as easy as sidescrolling on your profile and clicking "Relays" . There is nothing preventing relays from speaking to eachother and it has already been pointed out that some do, through mirroring.
As a simple open protocol, if a relay begins censoring or if a 100x scale up in users occurs, both relay diversity costs and spam prevention through zaps and and subscriber relays, has been part of the design from early on (and tor).

From a user perspective or relay provider Nostr is just KISS. No email signup, host lock in, version compliance/updates. Just nsec/npub , json parse and go. If you don't see the elegance, i'm not quite sure how to describe the beauty any better.

You like ActivityPub. Do activitypub ! It does not need to be either/or. For me AP is an overdesigned make-work program for specialist, like Lighting Network or Kungfu. Nostr is the Brazialian Jiu Jitsu of social protocols. If you like larping at decentralization, do activity pub! If you are trying to survive an uncooperative street fight, Do nostr.

https://image.nostr.build/f073e407c4f792a491adc199a32a63ce86c508ed713a71329c7ac7ca91f2264f.jpg#m=image%2Fjpeg&dim=587x945&blurhash=%5E99ZNTOf%3FKV%3FISoQF%3A%3FJjCohS5Im%25OX0xwayNFWG%3DfR%23%252s%3AaeR-JN%24-W9X8bJV%3FNFW%3FS2smo3NaMwsYn%25S1s%3AsA9rsZNFjFt8j%3DIms%3FNFR*t8bY&x=bb7d897bec6171b0c5dce204d8e252000ca09f0feb3e8d4cb33e8856aa0aa407