Jami doesn't require a phone number, which is p2p. Xmpp (+ Omemo) doesn't require a phone number and it's federated... I mean, if a service is willing to rid of phone numbers, it'll do totally without them.

The challenge of having your device solve a nasty PoW that takes minutes would not deter most people: a timer once is better than evil captchas, phone numbers, etc. I don't understand why they use hCaptcha and not that.

phone numbers for spam prevention are a bandaid for a mediocre solution. the mediocre aspect being that it's totally centralized when it should at least be federated like SimpleX. SimpleX is the ultimate solution to be honest with you, it's federated, fast, extremely private and extremely secure.

It’s the signal metadata that they want to keep associated with an identity

They still can fulfill government requests for who is talking to who and how often