Your definition is present tense and makes the history of the Church meaningless. ALL magisteriums matter- past, present and future. The past magisteriums are dead - what is left? Doctrine. What is the Creed, but belief in God and TRUTHS? What’s another word for Truth, but doctrine?
Your overemphasis on the papacy is not catholic. Yes, he is our authority on earth, just like St Peter was head of the Apostles but lest we forget, St Peter didn’t start the Church or invent the Truths of our Faith - Christ did. Which means that Truth/doctrine exists OUTSIDE and BEFORE the papacy. Ergo, the magisterium/pope is not the end-all-be-all, but Christ is, who is Truth itself. And St Paul and St John did a heck of a lot more explaining of the Faith than St Peter did, at least what was written down.
We must obey the papacy, yes. We must believe what Christ taught as doctrine, yes. Normally these do not conflict, but if they do, we fall back to the source, which is Christ and PREVIOUS ORTHODOX teachings. The pope can fail, as Christ said to St Peter “Get behind me, Satan.” This is not scandalous, it was expected to happen, which is why Christ gave the Church infallibility, so that future, bad popes would be bound by PREVIOUS ORTHODOXY and prevented from leading His sheep into error.
Truth (doctrine) is authority. Authority (magisterium) is not Truth.