Nonsense. You are saying that sin belongs to human nature. Jewish and Christian faith has always said that we were created by God with a sinless nature but chose to sin and corrupted that nature.
The human nature Jesus took to himself in order to save us from our sins was real human nature in its natural nature, not its corrupted state.
Since we agree (I hope, for God’s sake you agree) that Jesus had a sinless human nature, why would having a sinful mother help him with his sinless nature?
It’s his sinlessness, his guiltlessness that saves us from our sins.
We don’t insist that Mary absolutely, metaphysically HAD to be sinless in order for Jesus to be sinless. We just say it’s fitting that God by his absolute grace through no merit of hers, gave her the same sinlessness he gave Adam and Eve. If Eve was sinless at the outset, why can’t the Mother of the Redeemer be sinless as part of God’s full of grace favor to her to prepare her for her great mission?
We don’t argue from “what has to have been in order for something else to be”—we just state what the Church seems to have known—that she was sinless (by grace) and that it’s fitting that she was, not absolutely necessary that she was. Some Church Fathers did disagree on this point and said she sinned here or there but the consensus was that she was (fact) sinless and that theologically, this makes good sense.
Your effort to say “it had to be this way” leads you into heretical byways you really don’t want to enter.
Sin is not part of human nature. It’s something we added. It’s possible for God by grace to make exceptions. He seems to have done it once and once only because He became incarnate of a woman once and once only.
“Since we agree (I hope, for Gods sake you agree) that Jesus had a sinless human nature”
We do not agree. Jesus was “fully man” but was able to resist the sins of this world because he was also “fully God”. We will not, in our human understandig, be able to fully understand what that was but if he did not posess the sinfull nature of fallen man he would not have been able to defeat Satan.
Seems to me there is enough Biblical evidence that the sinful nature is passed down through the man (Adam) ... not the woman. It didnt matter if Mary was sinless or not, Jesus would not have received the sin nature from her anyway. There is no reason to insist that Jesus had to be born to a sinless woman. He had to be born of a woman to be fully human ... and the Holy Spirit provided the means for that pregnancy.