Both premises are correct. The conclusion does not follow the premises.
Major: The Catholic Church cannot destroy the Faith. The pope cannot destroy the Faith when he speaks ex cathedra. The pope can destroy the Faith when speaking or acting as a private person.
Minor: V2 popes have only destroyed the Faith when speaking or acting as private persons.
Conclusion: V2 popes can be legitimate popes.
Just stop. You don't know what you're talking about. What you're doing is distinguishing the MAJOR, so you're not holding that both premises are correct.
Uhm, no, holding an Ecuмenical Council and promulgating a new Rite of Public worship (Mass and Sacraments) are not the pope speaking or acting as a "private person". This is the same idiocy as when you claimed that an Ecuмenical Council is not Magisterium.
Private person would be when Bergoglio is answering question on his airplane or spouting heresies to Scalfari.
You can argue that the teaching of V2 was not infallible, i.e. were just merely authentic Magisterium but not that it was not Magisterium. You can argue the same about the Pope's actions, but to claim that V2 and the NOM were the Pope acting as private person (vs. in his official capacity as pope) is utterly absurd.