You bring up something which should be clarified. Most if not all here, to my knowledge, are not accusing the SSPX, Resistance, or CMRI of being formal heretics. A formal heretic is one who rejects the authority of the Church. It can manifest itself in the rejection of a dogma of the Church while maintaining that one does not reject the Church, sure. But not when the Church allows one's position or "interpretation" of the dogma. And the Church has allowed the implicit faith view - certainly not condemned it while its voicing was manifest among theologians - for centuries.
Which gets us back to the issue of authority, the magisterium. Are you a Sede? If not, the magisterium has not only allowed, but promulgated, Vatican II errors for at least half a century.
Why could not the magisterium allow, if not promulgate, the errors of BOD then?
I'm not accusing them of formal heresy myself, but I see it as the logical conclusion of the hypothetical where implicit faith is refuted that simply. I say hypothetical because I think it's not so easily refuted as just quoting Trent, even if it may appear that way.
I definitely was a sedevacantist for a while, and I wouldn't call myself a sedeplenist now either. I have no idea really and I'm not satisfied with any position at present, so I just try to avoid it as much as possible, but if I was pressed to answer I'd say I lean towards sedeprivationism. I don't see the relevance here though. Every trad is willing to admit that Rome is full of heretics; +ABL, Bishop Williamson and others have even described many in Rome as believing in a false religion altogether. But if +ABL and co. were heretics too for flatly denying a dogma, that'd certainly be news.
I see what you're getting at with the theologian argument, but you could apply that to Novus Ordo bishops then too, couldn't you? When Bishop Barron says there is hope Hell is empty and the Vatican says nothing, is he in the clear?
To follow up on my last post, we (or at least I) am not speaking of heresy, but error.
One does not have to be "uneducated" or of "ill will" to be in error.
You don't have to be uneducated or ill will to be in error about something complex and difficult, but you would be one or the other if you denied 2+2=4. My point is that for educated clergymen to be in error in good faith about implicit faith, the issue would have to be much more complicated than is being concluded here. If it really is as simple as "no salvation outside the Church, ergo anyone who isn't visibly within the Church isn't saved"(which I fully admit is the simplest and most literal interpretation), then anyone who accepts implicit faith would either be ignorant of basic dogma or wilfully ignoring it. So how could well-educated bishops be accepting it in good faith?