Your post contains many valid points, but there is one little difference here...
I assume that you're talking about a *real* girl in a bikini. The biggest difference is that the real girl is, real. She can decide for herself whether to wear a bikini or not. She might or might not be willingly turning herself into a sex object depending on why and where she dons a bikini ( socially acceptable at the beach, not so much in town, and there are different "levels" of bikini as well... ).
ZSS is different because she was *created*, probably by a group of men. Sex sells, and it's indeed a factor that is considered in character design. You have the choice between sexual beauty, cute beauty or graceful beauty. If you make a character ugly, it automatically turns it into a social statement. Like Shrek. If Samus was a gay man, everyone would be on about how he's gay, for example. Ugliness and other such things are just things that don't occur in games, especially Nintendo games.
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So yeah, the point is that sexual attractiveness was purposely inserted into her design, unlike a *real* beautiful girl who just happens to look good because she has good genes and the time to take care of her looks ( the latter of which I'm not sure applies to Samus....
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).
They easily could have made her look like an everyday, run-of-the-mill woman. Now she looks like a Dutch showmaster. Eh.
I once designed a female character. I gave her freckles and some dark spots on her skin, and she automatically turned into a still-pretty *person*. It was awesome.