I honestly don't think "realistic body proportions" come into what makes a good female lead. She doesn't have to be a nun. Sexy can be good.
I can't think of what makes me like female characters, but if you look at Bella from Twilight you will see exactly who I'm not thinking of. Chick has very little personality, is whiney (she was complaining about how much it sucked that people were giving her presents), follows her man blindly and cannot see his faults, is obsessive and whose only goal in life is to get married at 18 and have kids right away. Where is the adventure? Were is the sassiness and the fun? Its quite honestly pretty boring to have characters like that.
I mean, of course I want to get married and have kids at some point, but not at 18. I love people with their faults, I don't ignore them.
EDIT: Now that I think about it, expectations for women have really flipped in the last 50 years. It seems that now it is expected that a women will go on and have a long career, not have kids till 35+ and even then continue working. What is not really socially acceptable is that a woman get married and settle down right away. I don't know what you guys think of all this. I personally don't mind, I'll be happy as long as I'm able to use my Japanese skills and I'm with my man. People have given me weird looks about it ("don't you want to explore? Why are you only with one guy?") but he's my best friend, and I'm happy. He's not tying me down, I can still have a career. I don't get it really.