I think we've had this argument before.

Kabuto has surpassed Orochimaru in pretty much every single regard at this point. He's a true snake sage making his snake powers better than Oro's. He's a hell of a lot better at Edo Tensei. And instead of wasting his time trying to take over a body with one Kekkei Genkai he wants, he's figured out how to steal as many as he wants in his own body.

Calling him his Shadow is like calling Naruto Jiraiya's shadow, or Sasuke Madara's shadow. He's his successor.