I'm very much of the same opinion, @john!
How the voice as a musical instrument is designed to work is the same for the general population with a human anatomy ie., the underlying physics that's enabling sound production. Just the technical capabilities, dimensions and applications of this instrument change across things like body type, understanding, language, musical tradition, emotional interpretation & so on.
This has led me to understand that there's room for learning, building & honing an underlying vocal technique(the way in which the voice works) that is capable of supporting a wide free range of diverse applications like different languages, styles, emotions, whatever the ears are capable of catching and choosing. Regardless of whether you wanna take the car to the park or over a ramp, the way the car works and how you operate it stays the same!
And this how is exactly where my focus lies; in those small but fundamental commonalities in how the voice works. By teaching my students how to look at their voice just as another instrument with volume, pitch, tone & expression being their 'controls', they are better able to connect with their voices regardless of language or musical direction.
You've raised some insightful thoughts and agree with you! Thanks for the comment bud.
Some may find this unusual maybe but I find this to be the most straightforward, objective way to offer vocal technique instruction & training that can cater to everybody!