...So, you're saying that Korea voluntarily annexed itself to Japan to avoid being invaded by either China or Russia?

That doesn't make much sense. If it wanted to remain free of invasion, why would it surrender its power to Japan's empire, an empire that then began systematically erasing Korean culture and identity, as well as economically exploiting its workers? To their credit, the Japanese did overhaul Korean industrial infrastructure, but what's the use for Koreans if it only benefits the Japanese?

It should be remembered that Emperor Yung Hui of Korea refused to sign the treaty, thus making it illegal. It's safe to say that Korea was bullied by a more powerful neighbor into surrendering its autonomy, especially after the Japanese assassination of Empress Myeongseong.