Huh? The pretty rainbow is a perceptual mathematical model. The reason is it looks nicer than the HCL rainbow is that, unlike a HC rainbow at constant L, it includes luminance in its model of perception
To clarify: commenter above states that the pretty rainbow "drops the perceptual uniformity that often makes HCL useful." My point is that you shouldn't claim one is more useful than the other without specifying the problem domain you're optimizing for. Also the language itself isn't helpful: "perception" is fuzzy by definition and we have two distinct positions on what "uniformity" means. You've now added the magic word "model" to the mix. https://en.wikipedia.org/wiki/All_models_are_wrong
If any of this were obvious, Adobe wouldn't have stupid color pickers and I wouldn't have three wildly diverging ways for adjusting audio volume and light levels in my home.