Professor Grillo: The first question contains numerous inaccuracies that undermine the very meaning of the question. I will try to illustrate them one by one. Those you call “traditionalists faithful to Rome” are actually people who, for various reasons, are at odds with Rome, and not in a relationship of fidelity. The point of contention does not simply concern a “ritual form” but a way of understanding relations inside and outside the Church. It all begins with the misunderstanding generated (in good faith, but through a completely wrong judgement) by the Motu Proprio Summorum Pontificum, which had introduced a “ritual parallelism” (between the Novus Ordo and Vetus Ordo) that has neither a systematic nor practical foundation: it is not theologically sound and generates greater divisions than those that were present previously. The idea of “fidelity to Rome” must be challenged: to be faithful to Rome, one must acquire a “ritual language” according to what Rome has communally established. One is not faithful if one has one foot in two shoes. Having demonstrated this contradiction, the merit of Traditionis Custodes is that it re-establishes the one “lex orandi” in force for the entire Catholic Church. If someone tells me he is faithful at the same time to the Novus Ordo and Vetus Ordo, I reply that he has not understood the meaning of tradition, within which there a legitimate and insuperable progress that is irreversible.
https://blog.messainlatino.it/2024/06/interview-with-prof-andrea-grillo-on.html