The Internet itself is our modern, expansive, efficient, and general purpose peer-to-peer network
well... in theory, i suppose; but in practice it's really not, not in the sense i mean, because its infrastructure is hierarchical. for most individuals (not corporations), two agents can't just exchange packets directly; they are routed through a corporate point of presence, network access point, backbone router, and so on. it becomes seriously difficult to actually maintain any meningful "sovreignity" over that data. and there are serious efforts in the US to legally curtail one's options for maintaining anonymity. (e.g., rule 41*)
so, we come to mesh networks and so on.
i'll be the first to admit that the design and adoption of decentralized services is criticial as well - and something we're well behind on as you say - but it's not sufficient when the network infrastructure itself is increasingly being used as a means of surveillance and control. and unfortunately i think that trend will accelerate, whether we're informed about it or not.
@ngwese thanks for the peering link, eye opening indeed! there's a lot to think about down that rabbit hole... also, when you speak to the cost/effort of maintaining indvidiaul infrastructure components - this is something i immediately thought of when i read the OP, and fumblingly tried to suggest: data centers and the network hierarchy exist because of economies of scale; from my rather naive perspective it seems difficult for a truly decentralized network to stay efficient. and if it came to it (somehow), i wouldn't insist on anonymity at the cost of energy efficiency.
anyways, the OP and the discussion here is mostly about services; anonymity and security aren't the primary concerns; i've brought up the point and don't really wish to derail things any further.
(* in a nutshell, this rule allows judges to issue a warrant for search/seizure whenever “the district where the media or information is located has been concealed through technological means." it went into effect in december 2016.)