I just returned from France where I was able to spend a day observing PJ with one of his athletes sessions. He also said the same thing about cool down. Maybe he will have time to comment more. It was along the lines of allowing natural adaptation occur and the slow cool down has an opposite effect as a speed session and could reduce adaptations.
However, there are times when a cool down might be needed to speed up recovery, such as at a championships with multiple rounds over several days, then do it.
After PJ mentioned it, I said my athletes don’t cool down either, but it is because we are getting kicked off the track or I have to go pickup my kids before daycare closes and I just tell the kids to go home.