It proves that Mary, rather it be by supernatural powers or whatever,
Not whatever, by the Grace of God.
Preserved, kept from, as in without it she would not have been sinless.
I don’t understand the objection or why it is worse. Do we not say that our sins are forgiven, forgotten as if they never happened by the Grace of God? Do we not strive to “sin no more” as Jesus told us and pray for the grace to be “perfect even as My Father in Heaven is perfect”?
Mary needed a Savior and Jesus is that Savior, she was saved from sin when she was created in her mother’s womb and by God’s Grace she remained without sin.
Just as we are saved from sin by Jesus’ sacrifice, so too was Mary but as it says, in a singular and unique way. And just as sin holds no power over us because of Jesus’ death and resurrection, it held no power over Mary from the time of her conception.
Hers is the same Savior through the same sacrifice and victory over death, just received in anticipation of her cooperation with God to bring the Messiah to His children.
It’s really not that hard to understand or accept.
As Uriel(sorry easiest way for me to type it) said here, God is the Creator of the time and space continuum, the entire universe. He is outside time and so is Jesus and not bound by it as we are. Therefore, if He chose to do for Mary what He does for us all when she was conceived, He can certainly do so.