I don't know if I would agree that Augustine's concept of original sin was faulty. I would agree most of the Western Church abandoned it in the 11th century. There are those of us who still believe in original sin.
I believe in original sin too. I don't believe it is what you believe it is. I believe it is lack of original righteousness and does not condemn to hell. This is one place where you interpret Augustine correctly and where my difference with you is a difference also with Augustine. Much of the rest of the time I'm with Augustine and disagreeing with you, who misinterpret Augustine on free will.