Well, the article is actually a pretty interesting look at gender-essentialism. More than anything, I think Le Guin's thesis is "I really want to live in a gender-free Utopia where changing Prospero's gender doesn't transform the way I read the character, and I'm sad that I don't."

A lot of her criticism comes down to the fact that 'male' is an unmarked state and 'female' is a marked one, and that characters' actions become strongly-marked when the swap happens. Which is true, it's just that I love to see what the change from unmarked to marked tells us about the way we mark gender, while she considers that a problem.

(But then, my most recent bulletproof kink in fic is the category I can't quite call genderswap, it's the story where the canon male character has always been female and all the other characters in the universe treat them the same way as in canon. It really needs a better name than "always-a-girl![character]", which is what it mostly seems to be called.)