The reality that most encryption enthusiasts need to accept is that true E2EE where keys don’t leave on-device HSMs leads to terrible UX — your messages are bound to individual devices. You’re forced to do local backups. If you lose your phone, your important messages are gone. Lay users don’t like this and don’t want this, generally.
Everything regarding encrypted messaging is downstream of the reality that it’s better for UX for the app developer to own the keys. Once developers have the keys, they’re going to be compelled by governments to provide them when warrants are issued. Force and violence, not mathematical proofs, are the ultimate authority.
It’s fun to get into the “conspiratorial” discussions, like where the P-256 curve constants came from or whether the HSMs have backdoors. Ultimately, none of that stuff matters. Users don’t want their messages to go poof when their phone breaks, and governments will compel you to change whatever bulletproof architecture you have to better serve their warrants.