Your interlocutor is begging the question, in favor of his claim. He claims in advance that he has this guarantor of accuracy in the "church" and in the "person" he so regards as infallible a priori. Which is entirely the doubtful (from the Protestant side) assertion. Noting the lack of such an "office" in OT times, thus claiming asymmetry, assumes the very point of debate.
In the days of the OT, the OT itself tells us that the priests were the teachers of the Law/OT, together with the prophets who proclaimed and (after the pattern of Moses, the proto-prophet) wrote down the Lord's Word as directed.
Jesus pointed not just the scribes and other teachers of the Law to that which was written, but by them the whole people were confined to that Holy Scripture. Picking and choosing from the OT was not allowed, as if some of it was merely "tradition." Rome's real claim is that Herself as "the" church perpetuates the inspired role of prophets and apostles who gave fresh revelations; ignoring that the OT people were to judge the prophets, whether they spoke in accord with previous revelation.
Rome fails this acid-test. Their extra-biblical commandments and doctrines have all the flavor of the Pharisees', which Jesus roundly condemned. Rome does not get to begin (except in her own mind) with her claim that she (or the pope) is now above all such assessments by the hoi polloi, which position she then uses to shut down the Berean approach once praised by the apostles.