While R&R simply isn't Catholic ... I think that the term itself, coined by Father Cekada, has been entirely unhelpful.
I believe that a form of D&R (Doubt & Resist) may in fact be a legitimate Catholic position, and it's actually what +Lefebvre himself held.
So, the difference is this, that you must at least entertain some doubts about the legitimacy of the V2 papal claimants. Per the pre-Vatican II experts in Canon Law, that suffices to exonerate someone from schism for refusing submission to and communion with such a doubtful pope, i.e. doubt suffices to justify resistance.
R&R on the other hand affirm that it's certainly true that Prevost, Bergs, and their predecessors are Popes, thus the "Recognize" part, where i advocate a return to "Doubt" and Resist rather than "Recognize" and Resist.
So, here's the thing that modern R&R fail to recognize. Most theologians consider the legitimacy of a Pope to be dogmatic fact, i.e. something that's known with the certainty of faith. Now, the certainty of faith precludes doubt. That's why it's heresy not merely to deny a dogma but even to doubt the dogma, since one fails to accept it with the requisite absolute certainty of faith.
Well ... +Lefebvre, +Tissier, and +Williamson have all regularly expressed doubts about the legitimacy of various papal claimants. Consequently, they are not, as many R&R assert, sedeplenists, but, rather, sede-doubtists ... which is a term I coined largely tongue-in-cheek here on CI many years ago. If you had the requisite certainty of faith in this dogmatic fact of papal legitimacy, such as that which Catholics living in the 1940s all had about Pope Pius XII, that would preclude any doubt. And, of course papa dubius papa nullus. +Galaretta I know next to nothing about ... as if he's been living in a hermitage for the past 40 years, but the rest of them have all made statements calling into question the legitimacy of the Conciliar papal claimants.
So, then, as Father Schmidberger used to say in defense of non-sedevacantism, melior est conditio possidentis, basically a paraphrase of how "possession is 9/10 of the law", and it means that they give them the benefit of the doubt. Well, giving them the benefit of the doubt is ... to admit there's doubt, or otherwise you'd never have to say tht.
Then, given a doubtful papal claimant, to whom you may refuse submission without schism, there's probably no harm them in trying to obey any commands they issue "just in case" you're wrong in your doubt. Doubt is not the same as being certain of invalidity. This is analogous to the question about the validity of Sacraments. I do not have to prove invalidity with certainty to be able to and, in the case of the Sacraments, even obligated to avoid them.
So if the "R&R" wanted to continue to cling a non-sedevacantist position, they could legitimately adhere to the actual D&R position +Lefebvre actually held.
Now, the biggest issue SV have with R&R is in fact the implicit rejection of the Church's indefectibility, but if you read the statements made by +Lefebvre, he actually affirmed that the Pope could not destroy the Church to this degree due to the promises of Christ and the protection of the Holy Ghost. How then did he avoid the SV conclusion ... even if he did say it was possible? He questioned not the MAJOR of the SV position (as represented in sylllogism), but the MINOR, where he questioned HOW this could have happened. Is it possible the popes were blackmailed, for instance, or something else nefarious was going on where their acts were not free? Since the MINOR cannot be decided upon with the certainty of faith, then the conclusion can't be dogmtic either. That's the core problem with dogmatic SVism, the hidden MINORs and their failure to recognize the logical "weakest link" principle, that the conclusion can only be as strong or as certain as the weakest presmise, peiorem partem sequitur conclusio.
So ...
dogmatic SVism is wrong, since not all the premises are certain with the certainty of faith
dogmatic sedeplenism is wrong, since if it's dogmatically certain that they're popes, then you'd better be in submission to and in communion with them
moderate SVism is OK, since you could even say that you consider their illegitimacy to be morally certain
moderate sedeplenism, in the form of D&R, as articulated above, is also OK
But both the moderate positions are in fact simply the same type of thinking with slightly different emphases.
I hold that the moderate sedeplenism is more dangerous of the two, since it has the tendency to morph into what we see today, a rejection of the Catholic dogma that the Church cannot defect in her mission.
That's why I've long been an advocate of the "Sede-Doubtist" position, since it's a moderate form that avoids the grave errors of the extremes, both of which can be schismatic, and it permits a significant amount of leeway in their expression so that all Traditionl Catholics could easily unite with this "doubtist" framework, for all practical intents and purposes.