It seems to me that finding someone on a federation is as easy as on centralized systems. Do you have a use case in mind where centralization makes it easier to find someone?
Nope, It will only show accounts followed by local accounts.
Mastodon doesn't do any kind of per server search, And your "federated feed" is basically accounts on other instances followed by local accounts.
This makes hosting a private Mastodon server, for personal or family use, incredibly hard as discovery is basically impossible.
This can be fixed by using Activity pub relays, but guess what? Mastodon's official servers don't use them, which are the servers that really matter.
Its a big part of why I'm hesitant to use Activitypub, as I believe discovery is a big part of modern social media, and Mastodon absolutely sucks at it.
This is coming from someone hosting his own Matrix server.
It will search a subset of instances.
How do we know this to be true?
a) there is no central listing of all mastodon instances, or even all public ones.
b) it would take FREAKING AGES TO COME BACK because there are so damn many, you can only make so many parallel requests at a time, and you have to process the results from all of them.