The problem is not really concerning RGB to HSV or vice-versa (BTW if you have a working-well RGB to HSV code, i'm interested. I'm currently using the FastLED one ...)
The idea (and this is the main reason why HSV ever existed) is to get a easy and natural way to describe colors.
For anyone in the world it is easyer to say "I want a red, pale, not so bright" light, instead of a" #FFAA11" light!
When you are from a controller point of view, talking directly in HSV, allows to easily set a dim level (which is a major feature for a light, isn't it?), and a color (Hue). Devs like the Domoticz ones even dropped the Saturation at this time, but they are currently receiving (and could easily send) H(S)V values.
Also most (if not all) javascript color pickers are natively talking HSV.
About HSL vs HSV I think this not really important because it is just a story of different gamma correction / color space (if i understand well), and for devices intended as a Light (not as screen), color deviation is not a big issue. I just vote for the most used in related software (arduino lib + Javascripts color pickers), to try to match the requested color as accuratly as possible.
