I've been struggling with what you describe for a long-ish time in my readings. I love fantasy and science fiction. Those are my favorite genres and the ones I spend the most time reading. But after a while you get tired of reading the same thing over and over. Maybe the style is good, but it's as if it were just the rewritten wizards and dragons tale.

Why should fantasy be confined to the world of medieval Europe, which so many authors adopt as their stage?

I'm a writer myself and I've been trying to explore these genres. I haven't read of Ursula LeGuin, but from what you're describing, I'm going to have to pick up one of her books and give her a long read.

In others, she introduced strong female lead characters and placed people from different ethnic groups on the same footing, which have become staples of modern science fiction.

Maybe these things are cliché nowadays, but she did it first. Today all science fiction and fantasy movies have tokenized their cast, filling it up with the overused proportion schema of 1 black : 1 asian : 1 white : 1 hispanic and I'm leaving out the ethnic representation of native Aboriginals because they're actually not portrayed as often.

However, as I said, she did it first. Literature as a whole gives a step forward when authors like Ursula decide to change genres for good and take from the world as they see it and not as it is depicted by the mainstream context.

she did not avoid the classic European Middle Ages

But it's important not to forget that what may be considered cliché is also something that might find a valid place inside your works. Maybe castles are overused. Why not put a spaceship on top of it? I'm exaggerating a little, but from what you describe about Ursula, she was a great supporter of moving forward our old pieces, not letting our genre and our style stagnate due to tradition and fidelity.

A fan responded on Twitter that she had never read LeGuin and asked which book she should start with. Gaiman replied “Anywhere. She was that good.”

Thank you for the recommendation. I was about to ask that when I read that :P I'll go pick up one of her books. Thanks for the great post, @donkeypong, and for the inspiration. It will probably affect my writing style a lot now that I've read such constructive criticism.