No, that is not what I'm saying. I'm saying that this kind of configurability acts as an additional accessibility feature, and further could probably serve as a replacement for bespoke accessibility features these operating systems do have (like "dark mode" vs "light mode").

Arbitrary customization of color schemes may be useful as an accessibility feature for certain conditions.

However nobody has explained how they offer an accessibility benefit for any actual condition that isn’t covered by the existing accessibility features.

It would be good if someone could actually point to an example of this. Otherwise it really is just speculation.

General configurability of themes is definitely not a substitute for bespoke accessibility features, even though it might be a workaround in some cases.