Unfortunately for you and for Siscoe, the legitimacy of Francis as the rule of faith is NOT accepted peacefully and universally by the Church.
Such a condition would have applied to Pius XII for instance. Catholics everywhere accepted him as pope with the certainty of faith and never even gave it a second thought.
Many Catholics have disputed the legitimacy of the V2 Popes ... based on serious reasons that constitute positive doubt. Where there's positive doubt, there can be no certainty of faith. So, for instance, when +Lefebvre or +Williamson or even +Tissier entertained the possibility that illegitimacy MIGHT be true and say that some day it might be declared by the Church, the certainty of faith is immediately GONE ... by those very statements. If you have the certainty of faith, you absolutely cannot question it any more than you might question the dogma of the Holy Trinity. SSPX spokesmen have often mentioned giving the "benefit of the doubt" to the V2 papal claimants. With certainty of faith, there can be NO doubt. Consequently, that statement alone demonstrates that they are not sedeplenists. So this argument actually backfires on the SSPX.
Finally, universally accepted by WHOM? By a Concilair Church whose members (by their OWN polls) are at least 90-95% NOT Catholic, since they deny one dogma of the faith or another. That would be like saying that if an Arian "Pope" had been elected in the days where 90% of the Church had fallen away to Arianism, that Pope would be legitimate due to their "peaceful acceptance". Just as in that crisis, you would have faithful remnant Catholics disputing his legitimacy, so too we have had that for the V2 papal claimants.
Archbishop Lefebvre:
“The question is therefore definitive: is Paul VI, has Paul VI ever been, the successor of Peter? If the reply is negative: Paul VI has never been, or no longer is, pope, our attitude will be that of sede vacante periods, which would simplify the problem. Some theologians say that this is the case, relying on the statements of theologians of the past, approved by the Church, who have studied the problem of the heretical pope, the schismatic pope or the pope who in practice abandons his charge of supreme Pastor. It is not impossible that this hypothesis will one day be confirmed by the Church.” (Ecône, February 24, 1977, Answers to Various Burning Questions)
Does this sound like a man who considers the legitimacy of Paul VI to be a dogmatic fact? Absolutely not. When he says that "it is not impossible" that Paul VI was illegitimate, that clearly proves +Lefebvre did not hold it as dogmatic fact ... since the certainty of dogmatic fact would absolutely preclude the "possibility" of the contary.