My point is that we need to focus on Lutheran piety, uphold the best expressions as models, but not diminish other expressions of it in the process.
Now the congregation you described was obviously not worshipping as Lutherans. And you ask a good question: How would such a congregation make the "quantum leap" to the Divine Service? I wouldn't characterize the jump as that extreme, but it would be a challnege. Here's the path:
1 – The pastors & the elders need to agree to a vision as to how the congregation should worship and then uphold that ideal as they move toward that goal, teaching and encouraging all the way.
2 – Over the course of about three years, the following changes would be made:
a. put up a cross as a focal point for worship. ("Here I raise my Ebenezer, hither by Thy help I've come".)
b. move the altar to a more clear & central location, add a pulpit, and a font. These are the three basic pieces of furniture found throughout Christian history around the world.
c. have the pastor at least wear a collar. Garments evoking Revelation can come later when the congregation is more catechized.
d. using the existing musicians, introduce more Lutheran hymnody to the congregation via the LSB Guitar Edition; CPH's Hymns for the Contemporary Ensemble; and other resources.
e. teach the congregation that because they are in Christ, their song is the song of Christ, and so we heed what Paul teaches us in two of the few specific instructions about worship we receive in the NT: "psalms, hymns, and spiritual songs". Follow this by introducing Psalm singing in styles that are consistent with the existing way the congregation sings and with the musical vocabulary of the P&W band. These are available from many resources, including, GIA, OCP, and Liturgy Solutions.
f. teach the congregation about the Spiritual songs. what is 'spiritual'? "Of the Holy Spirit" (according to Norman Nagel). What songs are "of the Holy Spirit"? Easy – the songs elsewhere in the Bible: the Canticles. The Magnificat, for example is a "Spiritual Song". The liturgy is full of Spiritual songs, and so introduce them to the congregation. Perhaps one a season until they have learned enough Canticles do do a complete Divine Service.
At this point, this congregaiton might still sing their praise songs as an Entrance Hymn and for an Offertory or as a closing song, but with this patience pace they will within two years be singing a Kyrie, a Gloria, various Psalms, a Sanctus, and an Agnus Dei, along with good hymns for the Hymn of the Day and communion distribution.
Finally, by this point they should be getting so much that is based in our hymnals that they can move from projecting LSB resources onto a screen toward getting actual hymnals.
Perhaps as this three-year plan winds down this congregation might want to do other things, such as learn to chant Introits or Psalms, have choirs sing the Verse of the Day, etc. Or they might not. As much as I like having a corpus on the cross, processions, a pipe organ, chanting, full vestments, and other rich trappings of liturgical worship, such is not necessary.
If the congregation in question simply did the things I outlined above, they would be recognizingly Lutheran in 1-2 years and will have become habituated in a Lutheran piety within 3. They would follow the rubrics of the Divine Service, and the focus of the people would be on where Christ gives us His cross-born gifts through the Office of the Holy Ministry: the font, the altar, and the pulpit.
That wouldn't be "high church" or "low church". It'd just be Lutheran church. In a way that would be appropriate to their sanctuary and their people. It would be a church none of us would mind visiting, even as we appreciate the different customs of our home congregations.