That is completely false. If you breakdown any hitter who swings a bat the ball is off the bat completely before they even let go of the top hand. SO it does not matter if you let go of it or not because the ball is off the bat at the point of contact. That is why some hitters do or do not it's just a comfort or psychological thing. If I rake and don't let go of the top hand I'm still going to rake weather I let go of it or not. The top hand goes along for the ride any ways the lead shoulder is your power hand if anything.