Alright so I’m not an expert so I might not be explaining it correctly.
Federated Network: Multiple instances sharing content, such as Lemmy
Peer to Peer Network: There is no “instances”, just peers. Many peers sharing content. Every user is a peer. There is no server costs, because every device connected to the network is acting like a mini-server. It will cost your device some storage space and network bandwith depending on the how the software is designed.
Or do you think Centralized servers are still gonna dominate the future?
Look at the Zerotier vpn model. They have several instances hosted all over the world that the client app running on user devices initially contact. These instances are in essence federated even if they use a different term for it.
The instance then gives each client a list of peers and how to reach them, and the clients attempt to reach each other directly, bypassing the instance where possible.
Both models work together. There’s no need for locking into one and ignoring the other. Use the best tool for the job at hand.