That is not accurate to our experience. Mobile devices on cell networks see about the same amount of success with p2p connections as other devices. Mobile networks differ vastly in their behaviors when it comes to NAT traversal, and you can certainly find specific carriers that behave poorly, but it's far from the death of p2p that you describe.
That said, you _do_ need last-resort relaying, not just for the more difficult mobile networks but for all kinds of edge cases (e.g. the UC Berkeley guest wifi case I mentioned in the article). So in that sense, the purist argument is that p2p is impossible since you will always need to have relaying as an option. But the key is that p2p works well enough to make the relays economically viable to operate, and that _some_ connectivity is usually sufficient, even if it's not the theoretically optimal connectivity.
Plus, IPv6 continues to be deployed (and AWS charging for IPv4 is another step on that path), so while some CGNAT deployments work to degrade p2p, IPv6 in parallel is restoring better p2p connectivity than IPv4's allowed for decades. It's not all roses, but it's possible to be optimistic about a future where cloud servers aren't the only option.
I guess I'm just salty, that 100% of my users can't connect to 100% of my users, but that is only because I'm building highly local hobby projects, so I can't see the global picture where the % is a lot more sensible.
That said, you _do_ need last-resort relaying, not just for the more difficult mobile networks but for all kinds of edge cases (e.g. the UC Berkeley guest wifi case I mentioned in the article). So in that sense, the purist argument is that p2p is impossible since you will always need to have relaying as an option. But the key is that p2p works well enough to make the relays economically viable to operate, and that _some_ connectivity is usually sufficient, even if it's not the theoretically optimal connectivity.
Plus, IPv6 continues to be deployed (and AWS charging for IPv4 is another step on that path), so while some CGNAT deployments work to degrade p2p, IPv6 in parallel is restoring better p2p connectivity than IPv4's allowed for decades. It's not all roses, but it's possible to be optimistic about a future where cloud servers aren't the only option.