Yeah, this is all nonsense, made up to justify the R&R position. In actual Traditional Catholic theology, the Magisterium determines what is consistent with Tradition and what is not. This doesn't mean every single word that emanates from the merely-authentic Magisterium is infallible, but the Magisterium must be regarded as generally safe. If there are some minor mistakes that creep into the Magisterium, they must be respectfully challenged ... from within the Church.
This is not a question of infallibility but, rather, of indefectibility. If all we had was a problematic statement here or there in V2, that would be one thing. But we now have a completely corrupt Magisterium over 60 years which is leading souls to hell, and a public worship that is displeasing to God and harmful to souls.