Call me stubborn, but still, no. That document is mostly correct, except for where it states it’s merely an exercise of the ordinary non-infallible Papal magisterium. There are no grounds for such an opinion. My opinion is more strongly supported by the OS itself, Vatican I, and Vatican II. And yes, I realize that this is Cardinal Ratzinger himself I’m disagreeing with, and I don’t take that fact lightly. But I must insist. OS meets all the requirements of Vatican I, and there is no way to demonstrate otherwise. I love Pope Benedict XVI, and I hope we get another one like him for our next Pope. But on this particular letter, he writes an opinion, not a teaching, and so binds no one. I have not resorted to argumentum ad auctoritatem, when making my arguments only to Magisterial documents to support my point.
All those opposed to my position have done nothing but cite other authorities and opinions, but have not provided a single demonstration, whereas I have resorted to the principles outlined by Vatican I and the document on its own merits, and I have done so more than once.
And just so that we put to rest the notion that “confirming the brethren” is somehow limited to only the college of bishops (which it isn’t) in a strawman effort to distance OS from the supreme Petrine office:
…And this is the infallibility which the Roman Pontiff, the head of the college of bishops, enjoys in virtue of his office, when, as the supreme shepherd and teacher of all the faithful, who confirms his brethren in their faith,(166) by a definitive act he proclaims a doctrine of faith or morals. (Vatican II, Lumen Gentium 25)
Anyone can try to parse or spin it, but an honest reading, even within its full context clearly unites confirming the brethren with the office of supreme shepherd and teacher in a single breath. Brethren encompasses the entire body of the faithful, not merely the bishops.
So no. Opinions notwithstanding, I have sufficiently proven that OS meets all the Vatican I criteria for infallibility, without denying that the teaching itself is already infallibly handed down previously by the ordinary Magisterium. My point is that the two exercises of teaching authority are not mutually exclusive.