Yeah but even with the phone number “leaking” (only to the recipient) nothing else even comes close to it. If your standard calls Signal a privacy disaster, what kind of product would you expect people to use? Everything else either involves storing comprehensive metadata in plaintext or worse durable logs of all conversation and interaction. Prepaid SIMs are pretty cheap and outside the US most phones are unlocked. Emails are too easy to fake and generally abuse. Nobody has solved this problem yet.