> What is your example of an effective open network then?

I'm not sure there is one. But that's because I don't accept the idea that "likes" and "follows" are the best way to find content, or even a good way. If you do accept the idea that those should be your primary way of discovering content, which Bluesky does seem to accept, then decentralization becomes a more important criterion, and Nostr or even Mastodon is more effective that AT. Unfortunate about the culture on Nostr, though...

You could maybe build a system that I would think was better by, say, indexing Nostr using some kind of DHT. But you'd have to do some things to traditional DHTs to make them more attack-resistant. And maybe more things so they could scale to that size. Having "topics" like newsgroups or subreddits would be another approach, and could probably be grafted into pretty much any protocol.