OK I'm not sure if this belongs in the Feeneyism Ghetto or not 'cause its kinda a multi-faceted question.
So some people here believe that its absolutely clear that nobody pre 1600 or so believed in salvation for anyone above the age of reason that didn't explicitly affirm the Holy Trinity and the Incarnation, ergo Fellay, Lefebvre, Williamson, and almost every other traditional bishop is *objectively* heretical (albeit materially and not formally so) for going against that consensus. I've also seen at least one of these same people argue that this view of EENS/Florence is the ONLY foundational basis to object to Vatican II etc.
So here's a question.
Eastern Orthodox are gonna argue that the Florentine view of Filioque *objectively* contradicts the UOM (even if they wouldn't call it that) because its unprecedented in the first few hundred years of the Fathers. We of course are gonna disagree with them. But on what principle is this disagreement an issue of Formal as Opposed to Material heresy, while the EENS debates aren't? particularly in the light of Sedevacantism apparently being an option to deal with perceived deviation.
is it really just that they don't affirm Immediate and Universal jursidiction of the Pope in theory? If they theoretically affirmed that but just quoted teachings of pre schism popes condemning adding the filioque to the creed (I've seen some quotes, BTW, though presumably not definitive) and said "well you know what I guess the see has just been vacant since 1054, or whatever" instead of outright denying immediate universal jurisdiction could that just be material heresy? Heck what if someone did this same thing with universal ordinary jurisdiction *itself* and thus was a pre V1 sede or maybe even a pre Florence sede or something? I mean, I've never seen anyone say universal jurisdiction is *absolutely* necessary for all Catholics to know at the age of reason like the trinity is. And Old Catholics certainly argued that V1 went against the tradition of the Church? So why isn't that sort of thing *also* just potential material not formal heresy?
I realize the discussion is often about Buddhists or Hindus or whatnot and that's an important component of the discussion, but I feel like there's some weird implications here for other Christian groups, particularly those that would have some concept of authoritative tradition and UOM whether they call it that or not, and I'm not seeing how epistemically both Sedevacantists and Conciliarsts could be part of the same Church because its "just material heresy" but yet people who make good faith arguments for these other groups based on tradition are automatically formal heretics. What am I missing here?