You make a strong case against choosing music based on the readings as a norm.
Sometimes I strongly suspect myself of jumping for the Propers out of laziness more than fidelity - to avoid just such questions.
Choosing the music to match the readings almost always kills the singing of hymns as Catholics do not have a large enough core repertoire in almost all parishes to make it work
But you and hartleymartin seem to think that harmony with the readings IS a general characteristic of Propers.
Advent and Christmas: texts from Old Testament prophets (including David) in a restrained and lyrical musical style.
Post-Christmas: narrative texts drawn from the gospels of the day sometimes in an extravagant musical style.
Lenten Weekdays: an original series of communion antiphons,dating from before the time that Thursdays were celebrated liturgically and in consecutive psalm-number order; some of the series have had the psalmodic textsreplaced with texts from the gospel of the day.
Lenten Sundays and Holy Week: mainly psalmodic texts, but with a few gospel texts of striking depth and dramatic value.
Easter Season: New Testament texts, both epistles and gospels, the gospel texts being from the gospel of the day, but the epistles not from the epistle of the day.
For the time from Ascension to Pentecost, most of these New Testament pieces are actually borrowed from responsories of the night office.
Sundays after Pentecost: a series of texts centered upon themes of Eucharist, sacrifice, and harvest, placed in psalm-number order (though they are not consecutively numbered psalms), but including texts from the wisdom literature and the gospels; the series begins with four of the replaced psalm-based communions from the weekdays of Lent, proceeds to a series of Eucharist, sacrifice, and harvest texts, with a few concerning justice toward the end.
To participate in the discussions on Catholic church music, sign in or register as a forum member, The forum is a project of the Church Music Association of America.