I can't make sense of these power rating!

I just started binge watching stone ocean, I pay attention to tiny things, even pause and rewind to see things again. And one thing that's confusing me is Ermes Costello's stand ability ratings. It's essentially PERFECT? ALL As?? and one C in the rating while on the other hand a stand like Weather Report only gets three As, one B, one C, and one E HUH??

Is there a canon reason for this? Ermes Castello's literally doesn't even use her stand to "fight", even for menial things (EX: every time Jolyn would ask her to hold her stand string like that plane scene or before Jolyn went down that hole in the hospital literally the most no-brainer thing to use your stand for) meanwhile Weather Report over here gliding around in the prison, using his stand to actively fight and manipulating weather. Someone please break it down for me why one stand that's clearly stronger get a lower rating than another that just splits and brings back a thing and make it make sense!