While I’m opposed to opinionated validation as well, you seem to be missing the issue it tries to solve, which is the user mistyping their email address, not receiving the verification email, and either thinking everything is fine, or thinking that the process is borked, and in any case not proceeding and not becoming your customer. The goal of opinionated validation is to inform the user about an incorrect email address immediately when they are entering it, so they can correct it right away.