" Pope Benedict XVI, in his Letter to the Bishops of the World, accompanying the Motu Proprio Summorum Pontificum, made clear that the Roman Missal in use before the Missal of Pope Paul VI, 'was never juridically abrogated and, consequently, in principle, was always permitted.'
"But can the Roman Pontiff juridically abrogate the Usus Antiquior? The fulness of power (plenitudo potestatis) of the Roman Pontiff is the power necessary to defend and promote the doctrine and discipline of the Church. It is not 'absolute power' which would include the power to change doctrine or to eradicate a liturgical discipline which has been alive in the Church since the time of Pope Gregory the Great and even earlier. The correct interpretation of Article 1 [of Traditionis custodes] cannot be the denial that the Usus Antiquior is an ever vital expression of 'the lex orandi of the Roman Rite'. Our Lord Who gave the wonderful gift of the Usus Antiquior will not permit it to be eradicated from the life of the Church.
"It must be remembered that, from a theological point of view, every valid celebration of a sacrament, by the very fact that it is a sacrament, is also, beyond any ecclesiastical legislation, an act of worship and, therefore, also a profession of faith. In that sense, it is not possible to exclude the Roman Missal, according to the Usus Antiquior, as a valid expression of the lex orandi and, therefore, of the lex credendi of the Church. It is a question of an objective reality of divine grace which cannot be changed by a mere act of will of even the highest ecclesiastical authority."
I venture to add that, if Traditionis custodes is ultra vires, contingent and inferior attempts at legislation on the basis of what it appears to mandate ... for example, by bishops ... will also have no power to bind.