However I have found this not to be true. For instance, with the above image provided by Nicolas, turn on color calibration, make sure gamut compression is 0, negative values are unticked and adaptation is none (bypass) in cat, then in R tab, reduce R slider from 1 > 0.5.
We see our purple patch has changed from 152,155,199 to 56,159,200. Sure, changes in G and B channels are minimal, but nonetheless, all three channels have changed. Now increase G slider in G tab to 1.5. Values become 8,199,197. In this case, we have not just a dramatic change in G channel as expected, but R channel also.