I'm aware that the Council did express the desire for continued use of Latin. They also gave bishops the freedom and power to authorize and promote the use of the vernacular if they chose to. It would be difficult to honor the integrity of liturgy with any traditional Mass setting lacking a memorial acclamation, Amen, or gospel acclamation. But much of the church's musical tradition is no longer liturgically useful. I know of assemblies that do sing Latin, but they are, perhaps unfortunately, rare.
Most assemblies are more comfortable singing with accompaniment.
I just know from my own struggles to teach chant to choirs and assemblies, it is an uphill effort. Maybe worthwhile, but still uphill. I agree with your assessment of the Gloria. I also detest the responsorial formats common these days. It would be great if ICEL had more leeway in translating the English version of it.