I don't think he denies both aspects exist, he spent much of the interview discussing various examples where a great power clearly acted immorally. He just knows that if he says "Russia is acting immorally" that becomes the headline and thousands of other stories will be printed saying "Mearsheimer reverses former position, denounces Russia."

That's what the two people talking past each other felt like to me. A journalist trying to force him into a sound byte that ignores his entire position.