Great Principle or Human Folly?

Pope Francis promulgated an Apostolic Letter motu proprio (of his own initiative) on September 3rd, 2017, in which he revises a clause in Canon Law to more clearly delineate the powers to determine liturgical legislation and norms between the Pope and the episcopal conferences. Paragraph one reads

The great principle, established by the Second Vatican Ecumenical Council, according to which liturgical prayer be accommodated to the comprehension of the people so that it might be understood, required the weighty task of introducing the vernacular language into the liturgy and of preparing and approving the versions of the liturgical books, a charge that was entrusted to the Bishops.

But is it truly a "great principle" (magnum principium)? Is this principle based on truth or speculative theories?
My analysis:
Fr. Josef Jungmann's Corruption Theory is a fruit the Ressourcement movement and thinking. Jungmann's theory that the primitive liturgy was corrupted between the Constantinian and Baroque periods is dependent on upon certain historical conclusions that are not settled. In addition to his Corruption Theory his Pastoral Liturgy Theory also presupposes the Ressourcement ethic of anthropocentric liturgy centered in the EXPERIENCES OF THE FAITHFUL. This reliance on experience is condemned by St. Pius X in Pascendi gregis #7 and #14. His system also relies heavily upon modern philosophy (after all, he's a Jesuit) and a pseudo-historicism that is rejected in #30 of the same encyclical.
Fr. Jungmann is certainly an important voice in the Liturgical Movement and a luminary in contemporary liturgical scholarship. But his personal conclusions are not something Catholics are required to accept and much less rely upon as though this is the only cogent explanation for liturgical development.
The overestimation of a pristine liturgical norm that was lost after the Edict of Milan and was only meaningfully recovered with Paul VI's fabricated liturgy is based on the Documentary Hypothesis which since its peak in popular acceptance in the 1970s has been in steady decline since.
Jungmann's theories are dependent upon an ahistorical or even antihistorical understanding of liturgy and the role of the Popes in preserving it.
Lastly, the experiment in liturgy begun in 1963 after the signing of Sacrosanctum concillium has yielded none of the results promised by its theorists, chief among whom were Fr. Jungmann, Dom Beauduin, and of course Annibale Bugnini. In fact Cardinal Ratzinger concludes the Roman liturgy has collapsed:

"I am convinced that the ecclesial crisis in which we find ourselves today depends in great part upon the collapse of the liturgy, which at times is actually being conceived of etsi Deus non daretur: as though in the liturgy it did not matter any more whether God exists and whether He speaks to us and listens to us.
...But if in the liturgy the communion of faith no longer appears, nor the universal unity of the Church and of her history, nor the mystery of the living Christ, where is it that the Church still appears in her spiritual substance?"

And is it true that that these reforms were undertaken because the Catholic faithful did not understand the mystery of the holy sacrifice of the Mass because it was in Latin? In 1960, 75% of American Catholics attended Mass at least weekly. Today that figure hovers around 25%. Of that 25%, almost none are aware that the Mass is a propitiatory sacrifice the Son offers to the Father as the Divine Victim immolated in an unbloody manner on the altar at the hands of the sacerdotal priest in persona Christi. So what has this great reform-to-improve-comprehension actually produced?  And why would the Pope want to double down on such a dismal failure, if not for ideological reasons?

As far as the vernacular, the dogmatic Council of Trent (1545-1563) infallibly condemned liturgy in the vernacular only (Session 22, Canon IX). So what is really going on here? And what will the further balkanization of the Catholic Church do to its universality in creed and prayer?

"The vulgar languages are in continual change; often words do not have today the same meaning that they had yesterday, or at best have one meaning for one person and another for someone else. About these terms we can truly say with Sallust, "Vera vocabula rerum amisimus" (Catil., c. 52). We have lost the right words in these cases. However, the Latin language is not only the most organic and logical language that has ever existed, but, for the very fact that it is no longer spoken by the people, it is now fixed, precise, and unequivocal, and presents us with well defined technical terms which have already been consecrated by the Church as the fruit of long discussions and solemn definitions, terms which it would be dangerous to ignore."

- The Memoirs of Antonio Cardinal Bacci