My answer would be that the primary difference relates to content & design and achievement level. Overall, 5A programs pull from a larger pool of performers, which will generate more money to pay designers & instructors. Any time you can reduce the student-to-adult ratio, achievement *should* go up.
A 3A director, likely teaching on their own or with only one assistant, will play something that is teachable by 2-3 adults and student leaders. A 5A director, likely 3-4 directors plus hired techs, will be able to "divide & conquer" the teaching load way more and can design more and achieve more.
I feel like the sheets are set up in a way that will honor the differences in these situations.
But, I'm probably wrong.