I think they should stick to the “email provider” analogy. Whole paragraph should be something like:

The only thing you need to start interacting with the Fediverse is an account with one of the many providers, just like with email! Providers are freely available across the globe: pick one that suits your location or interests best! You can start browsing the content of nearly the entire Fediverse from whatever provider you choose. Don’t worry, you can always create an account with a different provider later.

You could add a sentence or two about where to find sensible defaults or link an article that explains the more subtle things.

I think the emphasis on instances (and not naming them the more familiar providers) hinders adoption.

But in the end it’s just as with email: providers, spam filters and clients. Some providers have stricter spam filters (~federation), some might prefer another client. Has there been any significant reason to deviate from that terminology?

Meaningful discovery is a major issue in adoption, though. Pro: no search/discovery algorithm that serves some evil plan of world enshittification. Con: no search/discovery algorithm.