Ok. I don’t know what that means though.
Diatonic doesn’t matter?
There’s no Bb in there. Please explain.
All music has a tonal Center, where the music is at rest.
In tonal music you get there by cadences that ebb and flow, tension and resolution.
In modal music you have primary chords. Which contain the modal notes. The notes that define them, and secondary chords which don’t. But no real tension and release.
Play G C D… it wants to get back to G after that’s your tonal center, your home. The rest is various shades of away.
Diatonic doesn’t matter because it’s chords they’re here to support the melody (the tune) and connect the chords before and after in a sensible way.
If diatonic chords would matter guitarists would happily ride the F note over the C or Am chord in a progression in C.
My example So What is in D Dorian. So it has the notes of C major but the key sig it’s written is Dm
Which doesn’t care that there’s a one note difference.
In other words minor has 4 notes useable between the 5th and octave and it’s still major.
We don’t call something it’s in D natural minor, D harmonic minor, D melodi Minor , D Dorian etc.
it’s in D minor.
Again thinking of 7 chords make the key is useless because by that logic resolving G7b9#5 to C would be impossible by going to C.
Using Fm7 as a sub for Fmaj7 in C same thing.
As I said they need to support the melody and make sense in terms of harmonic function.
Play B/G to C and it’s still in C.
Actually to hear the key all you need is to hear the bass movement.