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Well, that's really your opinion because, as this crisis has proven, God has allowed evil that is beyond everyone's comprehension. 


In the practical order (i.e. what we can see, hear and feel), the non-infallible Magisterium is corrupted.

Theoretically, R&R and Sedes argue away the practical corruption, and come to the same conclusion, from different angles.
R&R - The non-infallible Magisterium is corrupted but what matters is the infallible Magisterium which is still intact.
Sedes - The non-infallible Magisterium is corrupted but it was done by people who didn't have authority so it doesn't change anything.

Both sides explain away the practical evils, since there's no way to avoid them.  The reality is, the practical evils remain, just as the novus ordo/V2 church remains. 
1.  R&R minimize the evils by saying the Infallible Magisterium is more important (which is true).
2.  Sedes minimize the evils by saying the corrupted non-infallible Magisterium is illegal, null and void (which is true).

Either way, both agree that the infallible Magisterium is still pure, holy and unchanging.  Either way, the corrupted, fallible Magisterium is still a problem and still causing spiritual destruction.  Either way, both theories fail to fix the practical problems in the world.

Your assertion that the Magisterium can go corrupt, that the Church can promulgate a Mass that's displeasing to God and harmful to souls, corrupting the Catholic religion to such an extent that Catholics would be justified and even required in conscience to sever communion with and submission to the hierarchy ... that's both blasphemous and heretical and its guts the indefectibility of the Church.  In fact, the proposition that the Rite of Mass used by the Church can be harmful to souls was anathematized by Trent.