Taking science fiction as positing a technological change and then writing a story about how the world is given that change, Left Hand of Darkness is absolutely scifi. It wonders what one human society might be like if cut off for centuries or more after a diaspora. The ambassador in the story seeing if the world can be brought back into the fold is classic scifi. It’s even more nuanced because the ambassador narrator isn’t some emotionless ubermensch, but a sexist fish out of water.