It was written early in her career... Check.
Ursula K. LeGuin writes mostly Sci-Fi... Check.
Earthsea is Sci-Fi... Huh? Where do you come by this conclusion? It is very much not Sci-Fi.
Also, she has continued the Earthsea series recently. It isn't only an early carer writing. Check out The Other Wind (Book Five) and the Anthology Tales From Earthsea.
I watched the Earthsea series on the Sci-Fi channel and I must say that it was awful. They did screw up her ideas badly -- I liked very much that only the Kargish peoples, the Scandinavian-esque civilization were pale, the rest a range of colors from southern African in the southern regions of Earthsea to southern European in the north.
They also butchered the storyline and did introduce an unsettling sense of "duality" that wasn't present in the novels. There was never any sign in the novels that the path of the dragons or the humans was correct (though the humans changed their minds at the end of The Other Wind), and the "faith" of the priestesses was a belief in the power of something they did not know to be evil. Certainly no duality there.