Either the conciliar popes have not lost the Faith or they have not been the true successors of St. Peter.
I believe this to be an either /or proposition.
That's because you (and many others on this forum) incorrectly believe that the magisterium/Church is the 'rule of faith'. If you would correctly believe that Divine Truth (i.e. Scripture/Tradition/Dogma/doctrine) is the 'rule of faith' then when 1, 2 or even 90% of the clergy apostasizes, it is not a problem (a similar situation arose during Arianism). As long as Divine Truth is not officially corrupted, the Church is still pure and Christ's promise of indefectibility is still kept. However, when one looks at indefectibility through the lens of the hierarchy, which is composed of fallible men, then you have all kinds of problems and inconsistencies in your view because men are naturally full of problems and inconstant actions.
As Christ said "I came not to destroy but to fulfill." which shows us that Catholicism is truly the perfection of the Jєωιѕн religion. Christ founded the Church on St Peter, as the human GUARDIAN of the Faith, but the faith was not based on the papacy - it is based on the natural law and Divine Truth, which existed LONG before St Peter and the Apostles were even born. Therefore, to say that the 'rule of faith' is the pope, or the magisterium, or the hierarchy is to ignore history, to ignore God's plan for salvation over ALL of time, and to ignore the eternal aspect of the Church's truths/doctrines, which existed before time even was.