By the Magisterium we mean the teaching office of the Church. It consists of the Pope and Bishops. https://www.ewtn.com/faith/teachings/chura4.htm
Theologians, Bishops, and even Popes do not “make something Catholic” just by saying it.
Well....yes they do make things Roman Catholic.....though not necessarily Christian.
It's what gets Rome the non-biblical idea of the Immaculate Conception or that a piece of cloth will keep you out of the hell-fire....but only if you wear it the right way.
It's what gives rise to other false doctrines such as the "Treasury of Merit".
You're starting to sound like the Gnostics again.
It's not a group word or collective word for "the Pope and Bishops."
It's not a committee or body of people at all. (For instance, you couldn't say "The Magisterium is meeting this afternoon at 1:00 p.m.")
It's the office, the authority of the Popes (plural, going back to Peter) and the Bishops in union with those Popes.
For instance, you could say "The Magisterium is the Pope's limited authority to faithfully transmit the Deposit of Doctrine --- that is, to hand it on without any change in its sense and meaning, and to explain it --- and not to rescind it or oppose it."
And you could say, "If the Pope is writing about Friedman's Market Economics or stellar parallax, his opinions are outside of the Papal Magisterium."
And you could also say,"If the Pope is writing to argue with or refute the teachings of his papal predecessors, his opinions are outside of the Papal Magisterium."
Please read these examples of correct usage, and understand that we're talking about an office or authority which has limits and has particular content. We are not talking about particular individuals and their every opinion.
If you ever became a Catholic of a sort, I'd still be disagreeing with you, because you have the makings of an ardent, over-the-top ultramontane Catholic like William Ward.