So basically those 4 were to they respective nations what Gohoumei is to Wei or Riboku is to Zhao, and they probably only submitted to Chu because their nations didn't have the money and numbers to handle the war.
Of course, the greatest in a small country doesn't really mean the same thing as the greatest in a huge country and even if they compare themselves to the likes of Kanmei, Moubu was the one to slay him, so it isn't really a fortunate comparison in this situation.