Certainly the crux of the issue is that all TRADITIONAL CATHOLIC sides of the crisis have "defectibility" problems.
R&R: can the Church's Magisterium defect?
SV: can the Church hierarchy defect?
That's an oversimplification, of course, but the sedevacantists find it to be less of a problem vis-a-vis indefectibility that the Holy See should be vacant for this length of time than that the Magisterium can become thoroughly corrupt with error over the same time period. R&R hold the opposite view.
Of course, this is a debate among TRADITIONAL Catholics, i.e. those who actually think there are grave errors in Vatican II and that the New Mass is not Catholic. XavierSem keeps interjecting from the perspective that there's no grave substantial error in the V2 Magisterium and that the New Mass is not inherently defective and displeasing to God. That's why he's muddling up the question, because he's not a Traditional Catholic. He actually agrees with the SV major that the Magisterium cannot become this corrupt, and then he agrees with the R&R major that the Holy See can't be vacant for this long. So he's agreeing with the majors of BOTH positions, and he's stirring the pot because rejects the minors of both positions (i.e that the NO Magisterium and Mass are not Catholic). He's basically a conservative Novus Ordite and not a Traditional Catholic. So he continues to fan the flame of disagreement among Traditional Catholics, at one time appearing to agree with R&R, and at other times appearing to agree with SV.