Eeeek - I think your really 'over-thinking' this.
Colours are just digital values - so RGB 0,255,0 in 8 bit is pure Green.
When that value is seen on a Rec709 calibrated display it looks a certain way.
When the same colour value is seen on a P3 display it looks different... as the display will 'map' 255,0,0 to a different Green colour.
When grading pushing a colour can't go beyond the peak value, so 0,255,0 is max Green - there is no more.
And OOG LUTs can be made for any colour space.