I agree, the whole paradigm of activitypub instances being treated as little local web communities that can interact with one another from their respective websites in limited ways is very flawed if the goal is for it to catch on as an alternative to existing social media experiences.

Although that's not to say that paradigm is innately bad though, since it works fine for more tech-savvy people and is basically what hexbear has and works well with, but it's a total non-starter for the average social media user.

Personally I think that something along the lines of what you said is the only way activitypub will ever be able to exit the niche space it currently occupies. The user should not have to learn how it works whatsoever. Ideally the process of getting a friend to join should sound more like "Install this app or go to this website(which is a server-agnostic frontend), click register and pick a service provider(not an 'instance')" rather than "Find an instance, go to its website(which all look slightly different), create an account, and then inevitably end up with a disjointed mess of browser tabs on different instances because you clicked 'View the full profile on the original instance' while trying to find people to follow."

I'm not a developer, but it really feels like the fediverse movement is sort of trying to reinvent the wheel in a lot of ways. Also sorry for the long rambling reply, I'm bored at work.