There was discussion some years ago about tennis serves/swings. Many thought the students should train the forearm/wrist muscles for a better swing. The newer teaching is that the wrists actively do little to get good racket head speed. I'm sure there's been a similar discussion in golf.
I see both the club head and shaft lagging. Comparing his swing to the pitching motion, I see his arms acting like the upper arm of a pitcher. The shaft is the lower arm and the clubhead is the softball. The head lags behind the shaft until the arms decelerate and the energy transfers, or whips. With I/R, the clubhead rotates/whips from lag (palm up) to contact. The head continues to I/R past contact.
I see the ball lagging behind the forearm, which lags behind the upper arm. When the upper arm decelerates, the lower arm and ball whip through release with I/R. If the ball were held in-line with the forearm (or facing 3B) there would be less stored energy to tap.