> But he found that the speed with which students completed the quiz was a reliable predictor of their final course grade. Rote memorization of basic concepts does have some value in reducing the mental load and making it easier to focus on more complex concepts.

Maybe. Or maybe it's useless but skill at it is a good measure of how conscientious those students were in high school (e.g. the extent to which they bothered to do their homework). Or any number of other possible explanations.