This is the opposite of what Thomas actually says in that article:
Honor we show the saints is a certain profession of faith by which we believe in their glory, and it is to be piously believed that even in this the judgment of the Church is not able to err.
Cardinal Journet summed up the traditional belief on the matter in his book The Church of the Word Incarnate:
Similarly, certain pronouncements concerning contingent facts can be infallibly and irrevocably defined by the Church. She has infallibly declared that the five condemned propositions of Jansenius really figure in his book in an heretical sense; in the canonization of a saint she pronounces infallibly on the holiness of a human life; in giving final approval to a religious order she declares that the new Rule, in virtue of its general tenor—not merely on account of the three vows—is calculated to lead souls to perfection; she can declare infallibly that such and such a treaty is unjust or that a given contract is usurious or simoniacal. And indeed, if the whole Church could be deceived in appreciating how the burden of a book—Jansenius', for instance—stands to that of the Gospel, she could no longer teach men infallibly the doctrine of Christ; if she could go astray in appreciating a life—St. Teresa's for instance—or a monastic rule, or a treaty or a contract, as related to the Gospel teachings, she would no longer be an infallible guide to sanctity, which is nevertheless the ideal of Christian life.Theologians are unanimous in recognizing the infallibility of the Church in the above-mentioned matters. Many make it itself a point of faith. At the Vatican Council a canon had even been prepared with a view to the solemn definition as an article of faith of the doctrine that the infallibility of the Church is not "restricted simply to what is contained in the divine revelation", but "extends also to other truths necessarily required to ensure the integrity of the revealed deposit".
Canonization is, in fact, clearly an ex cathedra judgment:
For the honour of the Blessed Trinity, the exaltation of the Catholic faith and the fostering of the Christian life, by the authority of our Lord Jesus Christ, of the holy Apostles Peter and Paul, and our own, after due deliberation and frequent prayers for the divine assistance, and having sought the counsel of our Brother Bishops, we declare and define that Bl. Pio of Pietrelcina, is a saint and we enroll him among the saints, decreeing that he is to be venerated in the whole Church as one of the saints. In the name of the Father, and of the Son and of the Holy Spirit.
The Pope is using his authority, but after due deliberation and frequent prayers for the divine assistance. This planned step would be going against due deliberation. How can you defend this action!?
Journet is not an infallible source. Theologians are NOT unanimous that canonizations are infallible. The Catholic Encyclopedia merely states only that "most" theologians support this view. And St. Thomas states it is something "to be piously believed." (But then again, Thomas never lived during the pontificate of JPII.)
I'm afraid it's not. And don't abuse the writings of the fathers and Saints. That's more you have to answer for, not to me, but to God.
We, as Catholics, want to believe that when Holy Mother Church proclaims a Saint, that they were Saintly, in fact. We look to the example of the Saints. They're our guides in the one question we have to decide in this life - for God, or against, and if for, what are His rules for us? what then, in other words.
If the Pope wakes up one morning and says, Kofi Annan is now a Catholic Saint, even you might hesitate to call that an exercise of the Extraordinary Magisterium. I, and all Catholic, and those you quoted, have a much lower, and much more reasonable and holy threshold. There are procedures. There are miracles to consider, and so on.
You toss all that, and the Pope wakes up one morning with Kofi on his mind, and you just keep digging yourself deeper, instead of obeying The Church in her time of historic distress.