Right, according to the principle of R&R, the Church could theoretically become thoroughly corrupt in the 99% of her doctrine that hasn't been infallibly defined. That's just flat-out wrong. Magisterium of the Church can never become thoroughly corrupted like it would be if it were still operating through the Conciliar Church.
R&R doesn't generally deal in theories regarding the Crisis, or the exotic explanations or future predictions that sedevacantists often provide, or which sometimes speaks of doom for anyone who will not see it their way.
We accept that there's a Crisis that we cannot really do much about, except to try to keep the Faith as best we can, and to try to keep informed about important matters.
Sedevacantists, for the most part, believe that if only they can get all trads on their side, then the Crisis will somehow go away, as if the solution is only a human one.
Fr. Chazal also wrote this:
"An important Roman principle remains: "Non Nocere" (do no harm). It was perfectly understood by Archbishop Lefebvre, who retained whatever could be retained of today's Papacy and rejected ever more clearly, especially after 1988, the pestilence of heresy.
The Papacy is of Divine Institution (can 100.1), it still serves a purpose until the end of times. By reducing it to a cardboard level, a Pandora's box is being opened."