I asked if you believe that there is a possibility the Conciliar popes are declared false popes in the future. You said, "absolutely". Why do you think it is absolutely possible that it could happen? Would you say the same regarding Pius X, Pius IX, Leo XIII, etc., or is there something different between them and the Conciliar popes?
So, anyone who says that does not hold to the legitimay of the Conciliar papal claimants with the certainty of faith. That would be like saying I believe that in the future the Church might reverse the dogma of the Immaculate Conception. If you say that, you don't believe in the Immaculate Conception with the certainty of faith.
If they would only have the introspection to realzie this, and then invoke the principle that any well-founded doubt regarding papal legitimacy can absolve someone of schism for refusing submission, i.e. shift over to a "Doubt and Resist" type of position, we'd be much closer to a kind of unity among Traditional Catholics, not an operational unity, but at least where Trads can recognize that we're merely divided by a difference of opinion.
But those like Stubborn will refuse to take that out and will continue to insist that the Church can become so corrupt as to lose its notes, and to require a refusal of submission and communion in order to keep the Catholic faith. That's where they show themselves to be pertinacious heretics.
I've appealed to "R&R" in the past to consider adopting Father Chazal's position, which does not labor under any problems for Catholic ecclesiology ... but they refuse, against steadfastly clinging to their heresy.
One could adopt SedeImpoundism (Chazal), Doubt & Resist (+Lefebvre), or some other variation (e.g. where Montini was pope but his acts were invalid because they were not free, but forced by blackmail), etc. There are a fair number of ways to avoid committing to that ultimate evil of SVism without destroying Catholic ecclesiology and losing the faith.