UR
In his book "The Reform of the Roman Liturgy", Msgr. Gamber never in any way calls into question the validity of the New Mass due to any changes in the ritual of the Novus Ordo Mass. His basic contention is that the new ritual of the Mass is just that, a new ritual of the Mass. Thus, for all practical purposes the Roman Rite is dead, when not using the Roman Canon in the Novus Ordo Masses. Because of his knowledge of ecclesiology and sacramentology, Gamber never insists that the new ritual of the Mass is somehow invalid.
On the other hand, there must be said something for the defense of the authority of the Catholic Church, which has the power to guard and protect the sacred liturgy. Msgr. Gamber does not question the papal authority and power to determine liturgical reforms. He does question, however, whether or not it is really in the best interest of the Church to radically interrupt what were traditionally the liturgical rites of the Mass, which had roots for over a millennium, not to mention the very center of the liturgy, the Roman Canon (which had been determined already, almost in its entirety by the fifth century, even before the time of Gregory the Great). Gamber questions the prudence of the Roman Pontiff in discarding these venerable traditions without sufficient cause, especially when there had been no outcry on the part of the faithful, before, during, or even after the Council to discard or destroy any of the elements of the Roman Rite. And even if there had been a general outcry for change, there still would have been on justification for destroying a veritable work of art, a treasure for the Church for all time.
There are 17 oriental rites (give or take a few variations), that are officially recognized by the Church, and whose development also hearken back to the ancient Church. Would you have all of these rites replaced with the Tridentine Rite?