Lulu was always targeted in my party which used to wind me up alot. She's got an amazin magic defence but that don't mean jack when the majority of enemies rely on physical attacks. Rikku starts off with low HP but look where she starts on the spere grid... after a few levels she's already matching everyone elses HP. For me she easily matched Tidus for his HP who was second to Auron by not very much. As for Kimahri..i barely used him but was amazed by his magic defence when i did pull him out. He would easily survive three hardcore magic attacks with only 1500HP whearas Auron with over 8000HP would be K.O'd by the same attacks