A false dilemma regarding development of doctrine

At Michael Liccione's blog Philosophia Perennis, Iohannes presented a dilemma as a criticism of the Catholic notion of development of doctrine. Iohannes has since referred to the dilemma, as though the dilemma is not a false dilemma. But the dilemma is a false dilemma. Here's the dilemma, in my own paraphrase:

If the Magisterium can see that the proposed doctrine is implicit in the deposit of faith, then the Magisterium can in principle see more than other informed persons, and so tradition is no longer public in a meaningful sense. But if the Magisterium cannot see that the proposed doctrine is implicit in the deposit of faith, then the Magisterium lacks warrant to declare that the proposed doctrine is implicit in the deposit of faith.

This is a false dilemma because the consequent of the conditional in the first horn of the dilemma does not follow from the antecedent. Just because the Magisterium can see that the proposed doctrine is implicit in the deposit of faith, it does not follow that the Magisterium can in principle see more than other informed persons. The ability of the Magisterium to see that the proposed doctrine is implicit in the deposit of faith is fully compatible with other informed persons also seeing that the proposed doctrine is implicit in the deposit of faith. And since the consequent of the conditional in the first horn of this dilemma does not follow from the antecedent, therefore it does not follow that "tradition is no longer public in a meaningful sense". A dilemma is shown to be a false dilemma when one of its horns can be embraced by those holding the position against which the dilemma is directed. I have shown that Catholics can embrace the first horn of the dilemma without facing the negative consequences Iohannes claims follow from doing so. Therefore, I have shown that the dilemma Iohannes presents against the Catholic notion of development is a false dilemma.