the way i looked at it is destroyers right

but when genma said that about sasuke, what i interpreted was hey your as strong as most chuunin go make yourself useful

shikamaru is a thinker so that makes him a chunnin cause he's a good leader

sasuke is irratic and unpredictable he may do something that could hurt a mission more than help it, he just isn't cool headed or mature enough to be a team leader or chuunin just be cause he has the streangth