1.4.1 also relevant if hue is the same but brightness is different? #1781

The Understanding of 1.4.1 is exclusively about the fact that people who are color blind cannot distinguish color values (hue). It is not about contrasts when the color is the same. Nevertheless, in the discussions here (e.g. #1775, #875) 1.4.1 is also often applied when the hue is the same and the brightness is different. Color-blind people should probably have no problem with this (even though I am not an expert in this field). Hence my question:

• Is 1.4.1 only about hue differences? If so, do we need a new SC for sufficient contrasts (which currently only exists when it comes to adjacent colors (SC 1.4.3, 1.4.6 and SC 1.4.11) or focus (SC 2.4.11 and 2.4.12))?
• or is 1.4.1 in the end about contrast differences (see 3:1 exception). If yes: then shouldn't this be explicitly mentioned in Understanding (i.e. fixation on color blindness removed). In addition, the contrast requirements in SC 2.4.11 may then be unnecessary (see Does the adjacent color clause of SC 1.4.11 apply when focus changes swap colors but also are adjacent to the background ? #1775 (comment)).