Is this 'transition' not the 'chop'? Like what Barry is showing in the prior gif? To me it seems like a purposeful move. i suppose you can say its a reaction, but i think only because it comes after the care action. Maybe i am not understanding.
IMO, the swing starts at the hand pivot when you decide to swing. From there you need to get the barrel to the ball, but i am feeling the hand path is the most important part of this because the barrel will always follow the hands. The barrel then can also be called a reaction to the hands. In any case, like i said before, i am not into the arguments on phrasiology, just that i understand the actions happening.
If the hands don't stay up (on top of the ball) you can never 'swing down'. To me the ulnar deviation is the last action in the swing path to the ball starting from up and going down to. Depending on how early or late you are to the ball dictates if the barrel hits the ball still going down or if it hits coming back up. Not only timing, but without the proper posture my DD struggles to ever get back up. This 'down to' at least for what my DD just showed me today, can be missed and looks like the demonstrations that Swing Down across and down the torso more forward and flat.
I am not personally a fan of the chopping action, but if it works for you or anyone else, please continue with it.
In the chopping action that Bonds demonstrates, I get the impression that it is a purposeful movement. However, I do not think that is the case in the game swing. I believe the transition between articulations occurs naturally instead of being forced. That is why check swings are difficult. Your wrists are trying to prevent that transition from occurring, but sometimes cannot overcome the inertia created by the barrel.