I think they purposely gave Aeris some super awesome Limit Breaks and good stats and what have you so that you would use her and be all "man, she's so great whaaaaaaaaaaaaat" and then she dies and it would hit you harder. I didn't like her, but I like all of my characters to be at an equal level, so I was using her more than I would have if I just leveled up based on preference. She did have some useful limit breaks, but I still didn't like her, or like using her.