The Coronation Mass became a favorite of the Austrian emperors for coronations I suppose like Zadok the Priest for the English.

What are "reformed" Catholic ideas?

Please see the Catechism of Francis I

the [pleni sunt] from Britten's War Requiem.

Ha! Stokowsky was director of the Houston Symphony in my youth. The greatest example of musical butchery and vandalism was his arrangements of Bach fugues, etc. One could easily compose a new work for the canon if he got the itch. Trashing other people's work is ghoulish.

To say of several generations of the church, "those people got music totally wrong" strikes me as a rip in the communion of Saints.

Stravinsky, Britten, and Poulenc

We need an enthomusicology of 18th c. Catholic church music.

Annus qui of Pope Benedict XIV, written on the eve of the Holy Year 1750, is one of the comparatively few papal pronouncements that take up the role of music in the liturgy of the Catholic Church. The pope feared that visitors from north of the Alps might be scandalized by the condition of the churches in Italy and by the kinds of music performed at divine services. (In fact, the published memoirs of travellers reveal that they often were.) While asserting that music in church must first serve the glory of God, the pope also stressed the value of music for the edification and spiritual enrichment of the faithful – an important, hitherto unemphasized distinction that was to have a profound effect on the history of Catholic church music in the second half of the 18th century and beyond.
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The conviction that a reform of Catholic church music was urgently needed to purify it from the corruption of secular influence and triviality resonated widely in 19th-century Europe. It continued well into the 20th century, spreading to British colonies with significant Catholic populations and to the USA. Influenced by 19th-century historicism, many Catholic church musicians looked to the past for principles to guide the reform
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The Cecilians never quite addressed the issue of quality; thus their programme of reform tended to stress the absence of objectionable features rather than the presence of aesthetically outstanding ones.
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Spontini denounced musicians who performed music from operas to which liturgical texts had been supplied, and the organists who regaled their congregations with potpourris of popular operatic tunes fared no better. He recommended that the punishments imposed by Alexander VII as long ago as 1665 be meted out to the offenders: fines, removal from office, and even corporal punishment … Unfortunately, nothing ever came of Spontini’s prudent programme of reform.
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Questions of musical quality and aesthetic judgment continue to be debated, even though in the USA, for example, the National Council of Catholic Bishops rejected such considerations: ‘musical judgment really says nothing about whether and how this music is to be used in this celebration’ (Music in Catholic Worship, 2/1983). According to this view, ‘pastoral judgment’ rather than an assessment of musical quality is the decisive factor in determining the appropriateness of music for the liturgy. In his encyclical Dies Domini (1998) Pope John Paul II took a different view, defending the principle that excellence was to be demanded of text and music, both of which should be ‘worthy of that ecclesiastical tradition that, with respect to sacred music, lays claim to a patrimony of inestimable value’.