I don't think that the signed binaries are intended to prevent malicious binaries but rather instead to create an evidence trail once an malicious binary has be

I don't think that the signed binaries are intended to prevent malicious binaries but rather instead to create an evidence trail once an malicious binary has been submitted. Since you have to sign with a key that you have payed apple to authorize. Apple has the payment details that connect you and the signed binary together. In addition the membership has licence conditions that in turn allow Apple to sue you. The intent is a deterrent effect.