Ok, first regarding your three screenshots:
I think the first one still works and looks best, if you don’t use overly bright lights, this should be the way to go. Also my first dirty fix for avoiding the color shifting doesn’t seem good enough.
HSV vs HSL:
I don’t think this is directly comparable. The shader just uses plain RGB to represent the colors. The point is that the Albedo is multiplied with the other light so the question is more how to handle light brighter than 1. (Roughly speaking)
Converting ti a different color representation could be helpful here, but this is also expensive.
In the end you definitely got a point here…I will have another good look at the light blending before releasing the updated version of SuperPhysical.
Lastly:
If all lights are off, you shouldn’t see anything. I just downloaded the contribution and cannot confirm the behaviour in your screenshot. There is no emissive yet.