“I keep asking this because RCs keep making this polemical assertion”
You mean the assertion that if not for the Catholic Church there would be no Bible? Not an assertion, it’s fact. Something that drives Catholic-hating protestants crazy. Protestants can’t change history. Deal with the truth and move on.
Either you lack comprehension or you are avoiding the issue. Now read again very carefully,
The problem is not only that the church of Rome today is critically and otherwise different than the NT church, but regardless, the often repeated we-gave-you-the-Bible assertion, if it is to have any real import, seems to be arguing that being an instrument and steward of Scripture makes such the infallible authority on it, so that those who dissent from these stewards are rebels against God.
Affirm or deny???
Protestants can’t change history. Deal with the truth and move on.
The problem is that history is contrary to your version, as even RC research evidences , besides Roman forgeries , and thus the real basis for your assurance is that history is only what Rome says it is. Thus Manning's classic response,
It was the charge of the Reformers that the Catholic doctrines were not primitive, and their pretension was to revert to antiquity. But the appeal to antiquity is both a treason and a heresy. It is a treason because it rejects the Divine voice of the Church at this hour, and a heresy because it denies that voice to be Divine.. . — Most Rev. Dr. Henry Edward Cardinal Manning, Lord Archbishop of Westminster, “The Temporal Mission of the Holy Ghost: Or Reason and Revelation,” (New York: J.P. Kenedy & Sons, originally written 1865, reprinted with no date), pp. 227 .
Rome has attempted to conform history to support her, and you are supporting lies. Deal with the truth and move on.