im considering the possibility that the performance reviewer is harder on the overqualified candidate for any subjective assessment because expectations are greater or the goal of the lukewarm assessment is to motivate or challenge more capable candidates. an underqualified candidate only has to keep up to pass subjective assessment and the motivation is built-in

many people are immune to basic motivation tactics but im surprised how many of my peers i see influenced by reviews which seem mostly motivational, and occasionally political, to me

Maybe not in the context of military as I haven't served, but in private sector reviews can often determine your bonuses.

if performance reviews are based on peer feedback likely this - https://en.wikipedia.org/wiki/Crab_mentality