A man’s not a great poet just because he knows a little grammar and doesn’t violate usage.
What is missing than? Talent? But what is talent precisely? Undefinable greatness? Maybe just simple luck to stumble upon perfect lines? Some say a right moment in history, as exceptional skill alone might not be enough. God’s help? That’s probably overused. Right guidance? Audience? Right pen and right kind of paper? All of the above? Or none of them and hard work instead?