The swipe at Luther is unjustified. According to The New Catholic Encyclopedia:
St. Jerome distinguished between canonical books and ecclesiastical books. The latter he judged were circulated by the Church as good spiritual reading but were not recognized as authoritative Scripture. The situation remained unclear in the ensuing centuries...For example, John of Damascus, Gregory the Great, Walafrid, Nicolas of Lyra and Tostado continued to doubt the canonicity of the deuterocanonical books. According to Catholic doctrine, the proximate criterion of the biblical canon is the infallible decision of the Church. This decision was not given until rather late in the history of the Chruch at the Council of Trent. The Council of Trent definitively settled the matter of the Old Testament Canon. That this had not been done previously is apparent from the uncertainty that persisted up to the time of Trent
It should also be noted that what Pope Damasus (and some other Roman bishops in the fourth, fifth and sixth centuries) declared in part canonical, Trent declared uncanonical, proving that Pope Damasus and the Decretum Gelasianum was not definitive as you portray it.
Cordially,
If you read my post again, I said that the canon was defined at Trent. It was declared by Pope Damasus but not definitive until Trent. Secondly, what Jerome, John of Damascus, Walafrid, etc. thought is all good and well, but they never enjoyed infallibility. Neither did Aquinas, who questioned the belief of the Immaculate Conception. Once Luther removed the problematic Apocryphal books, it became necessary to render final, binding definition of the canon. The declaration of the Magisterium is infallible - the opinions of even the greatest doctors are prone to error.
Luther's motive in removing the Apocryphal books was to render impotent the belief in Purgatory. The debate among Church doctors regarding the Apocrypha was of scholarly import, not a mission to refute dogma.