I see your point, but still think that an onboarding site that assigns you an instance from a pool that's seen as reliable might be sensible. After all, we don't want "one big instance", that kinda defeats the point of the fediverse.
Also, I feel the network effect is even worse for Twitter-likes. You're on Facebook for your friends/family, and you might convince some of them to move. You're on a Twitter-like to follow certain people, and whether or not they're on a different service is a crapshoot. And if they are, chances are it's Bluesky.