"Incoherency" is the inevitable result of the situation that the RCC found itself in after Vat. II regarding the ecumenical status of the post-schism Western councils, and thus the dogmatic status of their pronouncements.
Oh, I do understand why
there is incoherence... but that doesn't make it less incoherent.
By derogating this position, however slightly, the RCC opened the door to the possibility that maybe those councils really weren't ecumenical, and thus maybe those pronouncements really weren't dogmatic.
First of all, there's no evidence that any significant part of the RCC would accept that such a possibility exists. The RCC still teaches these dogmas as they were true and universally binding.
Second, if the pronouncements aren't dogmatic, then there is a very serious problem, namely that if these dogmatic pronouncements aren't really dogmatic, they are false and heretical. If papal infallibility is not dogma, it cannot be a theologoumenon- it is plainly false. The doctrine, by its nature, allows for no middle way.
As silly as this sounds, I don't see any other way they could have proceded, since making an abrupt about-face on matters of such consequence would have undoubtedly induced a new schism, without necessarily healing the old.
Well, the question is: what is true? Is Papal infallibility true or not? If it is false, then rejection of falsehood and respect for the truth should transcend any concerns about schism. The Saints did not hesitate to proclaim truth and condemn heresy, even if it alienated them from the majority.