Pffft, Sora could decide what was talent or not. He was Prince. "Really." He couldn't hit the target after three days, unfortunately.
"Are you sure you want my advice? I do not want to displease your brother." Sora would probably teach him things that may be efficient, or Balambish, but not what Corin would want Riku to learn. He didn't want to step on the older brother's toes.