Lennon and McCartney never actually wrote a song together. ‘A Day in the Life’ was the closest they ever came to collaberation. It splices two separately composed songs together. The good parts are the Lennon song (and sung by John.) The mundane lame parts are the McCartney song (sung by Paul.) I’ve always wanted to edit out all of Paul’s parts since they’re annoying, but I’ve never gotten around to it.
I misunderstood the gist of your question... I agree totally. Paul’s middle section of the song is the dead spot. Lennon’s opening and closing sections are its greatness.