Snow White was created using rotoscoping, an animation technique utilized by essentially videotaping a real person's actions and then tracing over them. Back when it was made animating a realistic human character was unheard of, Disney were firm users of the rubber-pipe limb technique. Snow White was played by Marge Champion, that's why she looks so much younger than the other princesses and has short hair. Marge had a professional dancer's body and hair is notoriously difficult to animate unless it's rendered as one solid mass or just cut short.
(Marge can be seen in action in this video: )
The unnatural proportions in the more modern pictures are down to stylizing in the animation medium, it's not unique to Disney. Dreamworks animation has just about all of its characters as stringy beanpoles with heads bigger than their waists but few ever complain and anime is a different story altogether. It's common in illustration to exaggerate features to make them more expressive. An animated character that looks too realistic usually falls victim to the Uncanny Valley effect, as in the character looks so realistic but still so subtly 'off' that it makes the audience uncomfortable. (See Final Fantasy: The Spirits Within for details.)
The idea that most of the princesses just wait for their man to rescue them is such a lazy interpretation and taken severely out of context. Ariel had a long-standing infatuation with the surface world long before she saw the prince, and when her father completely overstepped his boundaries by destroying her possessions, that was the catalyst that drove her to ask the witch for help. Picture it another way: let's say a Muslim teenager became infatuated with Western culture and her very traditional father discovered her collection of Hollywood DVDs and set fire to them, driving her to seek the help of people traffickers to flee the country. It's largely the same story, with or without a romance involved.
Belle's story is not as cut-and-dry as Stockholm Syndrome: The Movie. The Beast was never outright abusive, she originally stayed in the house to free her father and he lost his temper and scared her a few times but ultimately showed himself to be a good person. And he let her leave of her own free will, she also returned of her own free will. A more clear example of abuse is Cinderella's stepmother, there was deliberate malice in her actions whereas the Beast was plain antisocial and awkward.
And the question of positive role models is a falsehood. Lauding Mulan and Merida as positive while deriding Cinderella and Snow as negative is going against one of the basic rights of feminism, the right to be any kind of person you want to be. Not all little girls want to play with weapons or go on adventures. Some little girls want to fall in love and get married and live happily ever after. Some want to read books all day, some want to collect random odds and ends for their aesthetic purposes. There is no right way to be a person, as long as you don't go out of your way to do harm to another human being.
I'll cite a franchise that makes this message a little clearer: My Little Pony. Does your daughter like to grow flowers? So does Posie. Is she a daredevil? So is Firefly. Is she nurturing? Give her Baby Cuddles. Does she long to be more grown-up and glamorous? Give her Heartthrob. These can be applied to the princesses as well, for every Merida-like tomboy there's also a homebody Snow White baking pies or an artsy Rapunzel drawing on your walls.