I think the OP is implying that if we were all given as much grace as Mary was, and without the handicap of original sin, then we would have the increased freedom to avoid sin and do what is good. This would result in a better world for everyone, even God (if God loves us as in desiring what is best for us).
Is it fair to say Mary remained sinless her whole life because of the extraordinary gift of grace given to her by God?
If so, why does it have to be an extraordinary gift? Why can’t everyone have been given enough grace to avoid all sin? Why does God choose to allow people to be “born in sin,” commit sin and harm others for an entire lifetime, and then spend an eternity tormented in hell, when it seems like he could have just given everyone enough grace to avoid this all, freely. If Mary had free will and was able to avoid all sin, it was only because of her extraordinary grace. We are not** free to avoid sin according to the teaching of the church as I understand it (pelagianism). It is an entirely appropriate question to ask, why not?
Indeed, St. Augustine couldn’t understand why, for instance, Jesus chose to heal or forgive only a relative few in his time on earth, when he had infinite knowledge and power to do otherwise. One could excuse Jesus by saying he didn’t want too much publicity or similar, or that widespread healing would be detrimental to his primary message. BUT, it seems like God could have and should have created each of us with enough grace to freely love him and avoid sin.
Instead, we are BORN broken, sinful, and guilty of hell. Let that sink in. Just by being conceived, you deserve hell. Look it up. Original sin is a mortal sin. The Baltimore Catechism explains this directly. Though the new catechism says original sin “doesn’t have the character of a fault,” it is a direct reversal of what St. Thomas teaches in the Summa, precisely that original sin is in fact a mortal sin with the character of a personal fault. God allowed all of us to be created in this condition. But, he saved Mary. Why not everyone?
I don’t feel a particularly strong need to defend my assertion that God has not created the best possible world. I think anyone can imagine a logically possible better world. In fact, a world where just one fewer person is tormented in hell forever would be better. A world where just one fewer child starves to death would be better.
Certainly, a world full of people free from original sin and with the grace-filled freedom to avoid actual sin would be absolutely better.