You also need to make sure that UV scales with changes in luma better. It's a fine balance between washed out luma addition with fixed UV balance, and RGB multiplication that amplifies additive light to the extreme when making dark regions bright. Preserving natural looking skin tones is especially difficult when changing contrast.
My preference would be to hide all tools that might cause an unnatural look under advanced options for those seeing an artistic effect and show beginners the "hard to mess up" options with more automation and less fine control using basic sliders.
By, UV, you mean chromaticity? In the YUV color model, which is a linear transform from an RGB space, it gives very unnatural looks when changing Y without changing UV, I think: saturation would be all over the place. The way the shadows and highlights work right now, is indeed by simply multiplying the RGB tristimulus. You seem to know what you are talking about. Any good resources you are aware of that go into more depth on this topic? We can also discuss this on Discord in more depth if you feel like it!
See the final color as a first degree polynomial (while ignoring non-linear Gamma). PhysicalIntensity = DiffuseColor * DiffuseLight + Specular + StrayRadiation(removed in image signal processor) + LensFlare. Then an RGB multiplication will have a strange effect on the latter added parts. Your task is then to identify what's the additive part and what is a part of the multiplication (can be hinted from local histograms as a relation between intensity, saturation and variation) before compensating saturation accordingly. If an evenly colored surface stays even, then you solved the equation.