CMYK is an subtractive color model, it is not very understandable and definitely not intuitive for human color perception. HSL is much better for that. It all is not too revelant in the end result I think because those are just models and their software exposes certain aspects of colors.
Mixing pigments (ink or paint) can be done in CMYK because it is a subtractive process. It would have been realistic and something that anyone who has played with finger paints or crayons has experienced. (Although I agree that it's not very relevant to the end result, it would have been nice to see it in the discussion.)
We looked at a number of color blending algorithms that operate in the CMYK colorspace. None of them work well. Ultimately, colorspaces are designed to solve the problem of representing colors in isolation, not color blending.
CMYK is more intuitive than RGB but still not quite there. It is difficult to grasp that mixing a saturated pinkish color (magenta) with yellow will produce red. On top of that, if you add blue (cyan) it will produce black!
Printer cartridges are highly calibrated for this kind of mixing, if you attempt to do it with acrylics or oils you will get a dirty dark grayish color. This is because different inks have different opacity and reflect light in different ways (as the German research points out).