It's not such of what is shown than how it is shown. It works for the mother of everything chainmail bikini, Red Sonja, when paired with Conan, her male counterpart, they look coherent. They both kick ass and take names and you see her the character and not the bikini.
Of course that depend of the writer and the artist, it is easy to see if the story will be respectful of the character or not.
No you are right, the chainmail bikini isn't a no in all situations.
Red Sonja looks perfectly in costume for her universe where heroes just seem to be allergic to clothing. Her armor not really meant to be armor, but then again Neither was Conan's Fur Thong or his Circlet really meant to protect his head. It helps also that even though she was attractive, the movie was more focused on her as a character.
Heck Wonder Woman's costume (not her current one mind you) has been called both sexist and feminist... though in her case it is a one piece corset.
Xena looks both awesome and appropriate. Though I am biased because I absolutely Adore Xena.
But that is sort of the thing...
Anna from Tekken for example is a Femme Fatale character who clearly uses sex and her body to get her own way and her clothing and style reflect this. I have no issue with her because she is in a game full of great female characters that are all over the chart. (Tekken has issues with female representation, but Anna Wong isn't one of them).
While Soul Calibur slowly increased the sexiness of all its protagonists and is the source of what is known as "Sophitia Syndrome" because Sophitia's breast size actually increased with every installment... and features women with breasts of REALLY fantastical sizes (Dear Goodness Taki, you must have serious back problems being over 6 feet tall with giant breasts that look like someone shoved balloons down your shirt)... Yet the only character who even slightly justified her appearance was Ivy, sort of her story doesn't really seem to shed any light as to where she developed a fondness of dominatrix gear and whips, and MAYBE Taki, though her story doesn't suggest she does any femme fatale kills.
It is why there are a few rules of thumbs I make about a character when it comes to them and their sexuality
1) Is this character meant to be sexy?: For example is this a shy demure female character who wears nothing but a thong? or is this Bayonetta who is meant to be an over the top sexual female character?
2) Is this character more then just sex?: Does the character have depth or are they beholden to it?
3) Does the character's sexiness take anything away from their representation?: Does the way they are presented for sexiness purposes make them seem less competent or less part of the setting?
4) Does the game treat the character like Eyecandy?: This can actually be a huge one and honestly you can get away with a female character being stunningly sexy, even to the point of character contradiction, so long as the game is focused more on them as a character then them as eye candy. I call this the Lara Croft Effect or the Tifa Effect (Tifa being the one that has faired better in the popular consciousness). This involves the Camera a lot!