I'm struggling to understand why the sexualisation of Cortana/Sorceress is necessarily a bad thing.
I can honestly say that if these games instead featured sexualised male characters, they wouldn't appeal to me, but they would neither offend or upset me. Nor would they affect my enjoyment of the game.
It's not. It's okay for games to have sexy characters. What's not okay is if the vast majority of games have sexy characters. Think of it like any other form of media. Wouldn't it be ridiculous if the vast majority of novels went into a in depth description of women's tits and ass? Wouldn't it be ridiculous if the vast majority of movies had women wearing bikinis?
When we think about blatantly sexualized media, we know that it's divided by genre. Action movies and 70s comedies that are bound to have sexualized characters. There is no such division in gaming. Serious games, wacky games, action games, role playing games, they all have the majority of characters sexualized. As a viewer, we have every right to ask how this serves the product.
I really don't understand how choice is not important. Choice reveals context, and context plays an important role in whether or not something is sexist.
Maybe you're saying that choice without believable rationale isn't important? I'm more inclined to agree with that sentiment.
Context is important, yes. Character motivation is not important because a writer can make any character motivated to get wear skimpy clothing or get naked. If we have a female character who likes to dress sexily, that can either be an asset to the story or it can be a simple means to add T and A. Either outcome can come with the same motivation. What matters is purpose. Sex and the City, while problematic, has a character named Samantha who is a sexual character. This is part of her personality and serves the stories, because it colors how she interacts with others and it helps move situations along. That's different from Megan Fox in transformers just happening to wear revealing clothing.