I think that when you really get down to it, body image and self-esteem are not the real issues here.
First of all, it's primarily liberals and modernists who object to Barbie and He-Man, because they see Barbie as feminine and He-Man as masculine. Liberals and modernists want boys and girls to be practically indistinguishable from each other in appearance, and beyond that, in mentality, behavior, and everything else — and Barbie and He-Man don't exactly look alike.
Beyond that, though, there are some real problems with Barbie and He-Man.
For starters, Barbie isn't really feminine in a healthy sense of the word. She is not modest, not maidenly, but rather she is all about arousing Ken's prurient interest. she's an ambulatory invitation to sin. Most of her costumes are immodest, and even her physical proportions (her impossibly small waist and impossibly large bosom) are designed to evoke a heightened state of sɛҳuąƖ arousal. The toy is intended to teach girls to be "sexy."
He-Man is also immodestly clad, and exudes barbarianism. Clearly he is physically fit — a good thing — and can handle a sword, which can be a good thing, but still his masculinity is really a caricature of masculinity, much like Barbie's femininity is a caricature of real femininity. In the case of He-Man physical strength and aggressiveness are over emphasized, and wisdom, charity and the like are absent.
When you try to frame the discussion in terms of body image and self-esteem, it places far too much importance on body image, and on self-esteem.