@thornwill goodness that's a well researched post! That must have taken you quite some time to put that together well done.
Yes I think you're absolutely right as well, hairstyles need some attention. It also bothers me that hair colour changes with the style. My Sims have different styles for each occasion and there are some that actually change their hair colour by quite a few shades, either much darker or lighter. Then we have the do rag situation where it shows a totally different hair colour by design. We are missing highlights and more hombre shades and the styles that have those are quite limiting. I personally think they could add highlighted styles in the same way they've got black/brown with grey hair swatches. They could do the same to add highlighted shades if we can't have a colour wheel.
I'm really frustrated with my current Sim's hair because she has the high pony with the highlights but of course there is no other corresponding style. I took about half an hour yesterday changing the colour to try and match it with a down style that almost matches the up do so she's not living in a high ponytail all the time.
I'd like to see a hair overhaul, ooh and a Hemsworth as @JonaO703 suggests because I mean, great hair!