like "Also, in every color combination surveyed, the darker text on a lighter background was rated more readable than its inverse (e.g. blue text on white background ranked higher then white text on blue background)"?
yes it's all preference, vision is subjective, but being surprised that dark mode isn't best is in this context... weird.
Of your criteria is battery life, dark mode is most likely better
If your criteria is eye damage/strain, then IIRC the research is divided on this topic