Everything has to fire as one piece, back foot, back knee, right hip, elbow, throwing hand. Simplifies the mechanics and brings in the larger muscle groups.
Elbow in is not a myth. McBeth's elbow is relatively close to his body in that throw.
Am I completely misunderstanding, or are you advocating a lack of Separation in a swing?
I view "elbow in" like getting the disc close to the right pec. Something that happens in passing, and is forced.
If your worry is injury, I'm not sure I'd risk it. Even if you're using all the right muscles, your shoulder is still connecting the disc to those big muscles. I think we underestimate the amount of energy we load in our shoulders, even with basically zero shoulder rotation.
If your worry is soreness, just take it easy. Also, stretch.