NIP-65/Gossip Protocol solves this problem without needing a centralized aggregator actually, it intelligently figures out where content is from the people you follow.
More and more clients are implementing it, and it’ll make it so that you only need to think about relays if you want to pick where your posts go, but even that is optional technically.
aggregator relays are cool and all, but I don’t think it’s ideal for those to be core to the Nostr network, otherwise it just becomes a slightly different version of Mastodon .