Right now at least "federation" and "P2P" are still really different things. Like, a Hubzilla instance isn't P2P at all -- it is a regular website that a single fan pays to have hosted on a server in exactly the same way all other websites operate, so a user's risks (as far as I understand them!) really are exactly the same as a user's risks on something like Twitter. The person who runs/hosts the server has some risks, but they mitigate those by moderating the server. Which is why we talk about each individual instance staying smallish -- small enough that a single fan can afford to host and to moderate it.

I think literal P2P is important to fandom's future to address the costs of hosting, but whereas federation feels to me like a conceptual bridge to P2P in terms of distributing the load (instead of 1 person being Tumblr, 100 people are 1/100th of Tumblr with federation, leading to 100000 people being 100000/th of a Tumblr in the dreamy future) -- but the technology is legally pretty distinct.