Just for fun?
Every girl can shine when they are with the right other girls. But some of them are still slighlty better. But it's stiff fun to sort them and put them in tiny boxes for no actual reasons. It's just an excuse to speak of girls and why their are broken or not.
To gauge girls we can just use their stats, skill, abilities, synergy between their own abitilies, the place they can have in one or more specific archetypes of teams and how they can do what they are supposed to do.