Brother...its an email product though...if you can use Signal, use Signal.
The point is there is no requirement for emails sent between different proton accounts to be as insecure as they are.
This is something where there are known open source solutions that are just flat out better than what proton is using, and proton just can't be bothered. You can't fix the whole Internet, but proton just doesn't care enough to fix itself.
There is no such requirement. They collect them necessarily in order to function.
By default proton doesn't log IP addresses. They're just not needed. But when ordered to they do.