I may be wrong, but saying the words “Mystery of Faith” were handed down to us from the Apostles through Tradition (note the capital t) implies that the Eastern Churches are not Catholic since they lack in Tradition.
Saying that the Church erred in introducing or removing “Mystery of Faith” is a lot like saying the evangelists and St. Paul erred when their formulas don’t line up word for word; i.e., some have chalice as the predicate, others Blood. The theological opinion (supported by St. Pius X) that transubstantiation takes place at “This is My Body/This is My Blood” bypasses all this confusion over the exact words of Christ; all the rites are different, but they all have “This is My Body/This is My Blood” in common. And it’s just as simple as that; you don’t have to make it complex.
Maria