Studying diamonds hair from land of the lustrous is pretty hard
How could I even simplify this?
(I know I fucked up a bit with the lighting on the hair at the top)

You're overcomplicating the fuck out of it because you don't understand value hierarchy. You can simplify it into 3 values as you can see right there in your own references. Your Midtones, Highlights and shadows. If that's official art on the left then it looks like they just treat the colors as midtones or base color, then add highlight and dark values close to eachother to create the illusion of specularity or shininess.

>>7606403