Problem with standard R&R, and the reason why sedevacantists so violently (and rightly) reject it, is that they posit that legitimate popes can promulgate a harmful and defective universal discipline (Mass) and teach error to the Church in an order of magnitude where submission to the Magisterium can harm people's faith. In other words, standard R&R posits that submission to the Church's Magisterium can be harmful to the faith and that it can be required of Catholics to categorically reject it. In other words, the battle here is about the indefectibility of the Church and about our duty to submit to the Magisterium and Universal Discipline of the Church ... and not some quibble of opinions regarding what happens to a heretical pope.
Your idea of R&R is completely screwed up.
As a matter of Catholic fact, submission to the Magisterium is wholly necessary and can never be harmful to people's faith, to reject the Magisterium is to lose the faith. This simple foundational truth is part of the faith and always will be.
You imagine, as you said earlier, the Magisterium is both infallible and not infallible or as you said, "non-infallible magisterium", which is to say the Magisterium can teach both truth and error, then you accuse R&R of the novel term, "magisterium sifting". According to your idea of the Magisterium, how else are we expected to determine which is which without sifting?
If the Magisterium is as you say, then we ALL must sift the magisterium lest we submit to the non-infallible (read: error / non-binding) part of the Magisterium. We have no other choice, according to your idea of the Magisterium that is.
Then you toss in our duty to submit to the Magisterium and the Universal Discipline of the Church, which is to say we must submit to the whole Magisterium, both infallible (truth) and non-infallible (error / non-binding) Magisterium, yet you say to sift which is which, that is to say, to sift between the infallible (truth) and non-infallible (error / non-binding) magisterium is heresy. What you never do is tell us how else are we to know which is which without sifting? We cannot depend on the infallible part of the Magisterium to tell us because what we think is infallible may well be non-infallible - according to your idea.
As I said, you toss in our duty to submit to the Church's Universal Discipline which is derived from the Magisterium. Well, who is to say that today's Universal Discipline was not derived from the non-infallible (error) Magisterium? According to your understanding, it appears today's Universal Discipline is part of the non-infallible (error) Magisterium because obviously, today's Universal Discipline is riddled with errors and heresies - apparently you understand this because of that evil magisterium sifting, which you say is heresy.
Setting aside for now how this whole idea of yours obviously decimates the Church's indefectibility, this sufficiently sums up your confusion as regards R&R, Magisterium sifting, Magisterium, and Universal Discipline.