They took the CIELUV/LCH/HCL solid and compressed it into a sphere, similar to HSL on top of RGB. The L* (perceptual luminance) value is consistent across hues, it can also replace the 100/200/300 scale for design systems.
But even the CIE model has flaws, chromacity is inherently linked with brightness/luminance, no color model can change that. A more saturated/chromatic color will always be perceived as more bright than a less chromatic one at the same luminance. And in order to create a palette you need normalization, which will always weed out individual color defining peaks.
