I can't tell whether this is serious or sarcastic 😅

As far as the "global square" part of the equation is concerned: yeah, you're right! A firehose of public statuses requires indexing to work, as a basic foundational premise.

However, there's nothing preventing someone from standing up a PDS, opting out of the firehose / big graph service, and instead leaning on federation between individual PDSes. I'm not saying it would necessarily be a common use-case, but it's definitely not impossible.