I think you rushed your response.
First, it implies that the Reformers made new arguments. The argument was never made about novelty. It was always supported by quotation of the fathers and/or scripture.
Second, it implies that the Roman Catholics disagreed with Reformers to the extent that negates the Reformers position. They didn't.
Third, it implies that St. Augustine didn't speak on this and/or that the Reformers were not fully aware of what he said.
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Taking Point 2 first:
Rome in fact said the following around original sin in their initial "confutation of the Augsburg Confession."
"For the Apostolic See has already condemned two articles of Martin Luther concerning sin remaining in a child after baptism, and concerning the fomes of sin hindering a soul from entering the kingdom of heaven. But if, according to the opinion of St Augustine, they call the vice of origin concupiscence, which in baptism ceases to be sin, this ought to be accepted, since indeed according to the declaration of St. Paul, we are all born children of wrath
Eph. 2:3, and in Adam we all have sinned
Rom.5:12."
So it wasn't that Rome had an issue with original sin, but they argued that the sacrament of Baptism, would wash away the effects of it and that this is what St. Augustine wrote.
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Further, Lets see the talk of Augustine:
"Of the same import is the definition which occurs in the writings of Augustine, who is accustomed to define original sin as concupiscence [wicked desire]. For he means that when righteousness had been lost, concupiscence came in its place. For inasmuch as diseased nature cannot fear and love God and believe God, it seeks and loves carnal things. God's judgment it either contemns, when at ease, or hates, when thoroughly terrified. Thus Augustine includes both the defect and the vicious habit which has come in its place. Nor indeed is concupiscence only a corruption of the qualities of the body, but also, in the higher powers, a vicious turning to carnal things. Nor do those persons see what they say who ascribe to man at the same time concupiscence that is not entirely destroyed by the Holy Ghost, and love to God above all things.
and also:
"In the same-manner, Augustine also speaks, who says: Sin is remitted in Baptism, not in such a manner that it no longer exists, but so that it is not imputed. Here he confesses openly that sin exists, i.e., that it remains, although it is not imputed. And this judgment was so agreeable to those who succeeded him that it was recited also in the decrees. Also against Julian, Augustine says: The Law, which is in the members, has been annulled by spiritual regeneration, and remains in the mortal flesh. It has been annulled because the guilt has been remitted in the Sacrament, by which believers are born again; but it remains, because it produces desires, against which believers contend."
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I can also provide a couple quotes of St. Augustine, though I'm not at my house, so limited.
""For, surely, he who is still being renewed from day to day, is not yet wholly renewed. And to the extent that he is not renewed, to that extent he is still in the old state, etc""
"" The old infirmity is not taken away the moment a person is baptized, but the renewal begins with the remission of all sins. For although total and full remission of sins is made in Baptism, nevertheless, if there should occur at once also a total and full transformation of the person into permanent newness, I do not say also in the body, but if a perfect renewal could occur in Baptism in the soul, which is the inner man, the apostle would not have said: 'Although our outer man is corrupted, nevertheless, the inner man is renewed from day to day."
""Our vices which resist the law of the mind through the law of sin; their guilt, indeed, has vanished in Baptism, but the infirmity has remained."
And so forth.
So we are still back to what I said above that the east and west did not agree on this and took very different paths. The west understood that concupiscence (evil lust) was with us at birth (and before) and the question was really about what role did Baptism play in removing/negating it. All of which seems foreign to what you've said.