“Are you arguing that being the steward of Scripture makes them the infallible authority on it”
No, that authority comes from God.
No, that authority comes from God.
That also avoids the issue, as that is a given, and does not deal with the instrumentality which Rome claims, and since Scripture comes from God, then your statement renders the "we-gave-you-the-Bible" polemic meaningless. Thus go back and answer it again if this repeated assertion is to have any real import.
Either being the instrument and steward of Scripture means implicit submission to them is warranted, or they are another instrument whose Truth claims are to be ultimately judged by Scripture in ascertaining and establishing their veracity.