I say this as someone who has read SO MANY books by writers who never made it as writers, so they wrote writing books about something they weren't successful at. You see the same advice over and over about plot structure and characterization, and it usually amounts to nothing more than "just try really hard to be creative guys, okay?? TRUST YOURSELF AND FOLLOW YOUR DREAMS OK? GUYS?? OK???"
Even super awesome author Neil Gaiman fell prey to this - yes, he's amazing and successful and I love all his works. But he produced a Masterclass on writing that's the same old fluff you read in every amateur book on writing. He's great at what he does, but didn't have anything new to say, but wanted to say it anyways.
McKee's book isn't like that. It's a genuine masterwork, like when Scott McCloud broke down comics.