Nope. You are using that term totally wrong in this context.

A federated system is a system like email, where individual users use the system though a centralized entity of their choosing. Nostr is closer to that model, due to how relays work. You choose the relays you use, and other users also choosing to use those relays can communicate with you.

But it's not a very good federated system, as that aspect isn't made clear. So a lot of functionality is in practice centralized, as it only really works if everyone uses an overlapping set of relays. 

 There is one key difference though -- unlike email, a single message can be relayed by many different servers without loosing its uniqueness. As in... decentralization, you know?  

 What you're describing is redundancy, which email also has. Not decentralization. 

 Mmmm... no, it's not the same. 
I can send an email from different SMTP servers, but messages not coming from the "right" SMTP are nowadays mostly discarded. 
And even during the times when that used to worked the recipient couldn't verify its authenticity. 
And even if that really worked today then I won't be able to receive replies unless I submit myself to centralization (single point of failure, the postmaster.) 

See? You don't understand how it works.