A comment was made yesterday at Octoberfest that I mostly agree with: it's a crying shame that we have various texts of the ordinary, which really result in differing liturgies, not "settings" as they are misnamed.
But it is worth noting that in one regard, this peculiarity of LSB is actually deeply imbedded in Lutheranism itself. From quite early on, the great rimed hymn paraphrases of the Ordinary were treated as full equals to the straight forward prose texts (which mostly persisted in Latin, rather than German). If we were to drop for a visit to the Thomas Kirche in Bach's day, the Mass was held with great reverence and dignity. On the Sunday the good choir was at work, the Latin ordinary was sung: Gloria in excelsis Deo et in terra pax hominibus... On the next Sunday the "b-level" choir led the singing of: Allein Gott in der Höhe sei Ehr. The Latin Gloria or the German Gloria, they were thought of. Similarly, and even more shockingly so, the Nicene Creed. In either case, the priest intoned the solemn "Credo in unum Deum" to be followed by the so-called "Patrem" - one week the actual text of the Nicene Creed (Patrem omnipotem etc.) and the next week Luther's paraphrase "Wir glauben all in einen Gott."
Some argue from this that Lutherans were free to substitute ANYTHING for the ordinary and thus the ordinary doesn't really exist. But that's precisely not the case. Rather, a distinctly limited set of chorales came to be regarded AS the Ordinary. The idea that you would have a Mass without singing Kyrie was unthinkable to them! But the Kyrie could be one of the troped Kyries from the Middle Ages (Chemnitz cites the Kyrie Fons Bonitatis as the clincher in setting forth the Church's confession of the Trinity in Loci Theologici), a straight Gregorian Kyrie (though usually reduced from nine to threefold), or Kyrie, Gott Vater!
Now, what they were doing, in their own minds, was providing a vernacular setting of the Latin ordinary, but doing so in rimed paraphrase and using the chorale as the musical idiom. What they were not doing was saying that you can use just any old text. The depth of this rimed paraphrase tradition is always before me here at St. Paul's, where the great bell is inscribed around with "Allein Gott in der Höh' sei Ehr!" They didn't think of it as "just a paraphrase"; they thought of it AS the Gloria in Excelsis - the German version.
Thus, I believe that what the LSB did in part was to recognize this tradition as an authentic ascpect of our heritage (Divine Service, Setting Five) and one worth preserving; and also attempt a similar matter for English (Divine Service, Setting Four). The intention of either of these is not to suggest that one can decide to toss the Kyrie or the Agnus. It was rather to say that the Church has various ways to sing these texts, and straight forward prose rendering is one of those ways, and will, I would think, always be the touchstone against which the authenticity of the rimed paraphrases should be demonstrated.
P.S. No, Terry, I'm not addressing the matters of DS I and II in the above, as you will no doubt note... The real crying shame is that *the prose versions* do not agree!!! Here my touchstone will always be the Common Service, Divine Service, Setting 3 because it is a more faithful rendering of the Latin text. Note the apocopation in the Gloria in Exclesis and the paraphrasing of Lord of Sabaoth or hosts with "God of power and might."
P.S.S. Studying Lutheran liturgy vs. Anglican liturgy is always instructive too - because the one thing that screams out from the pages is how preoccupied Lutheran liturgy was from the get go with MUSIC. And it from the music that you can see why we have the two different prose texts of the ordinary in LSB: the COW desired to preserve music that had become dear and loved to many of our parishes.