..The seph was made from a diagonal angle, which might distort visibility of the actual movement made.
Keeping in mind that your questions were relative to the ceph of oblique perspective,'which might distort visibility of the actual movement made'. When that's the case, it calls into question why you expected it to yield an answer to the question of 'would he benefit from moving his jaw angles back?'. It's a demonstration of seeking answers to distorted questions which might yield distorted answers.
The link again for reference: https://www.instagram.com/p/BkDw1OoBQvo/?igshid=YmMyMTA2M2Y=
I think it’s quite evident that there was horizontal movement from the second picture, which shows the b/a from side profile and front view. I’m not sure how you are concluding that the jaw angles were not moved forward and that there is no blunting, since the picture from the front clearly shows a more roundish and less angular face.
So, now your question seeks out an answer to front and side views that you fail to link in your response and you're 'not sure' how I didn't see blunting from an oblique ceph your questions were based on.
From the ceph you introduced, I saw no telltale signs of an extent of horizontal movement that would yield blunted angles. So a question of 'should he move them BACK' can't be answered when a ceph used to ask the question doesn't show the jaw angle segment was moved forward.
I see the following here: drop down + horizontal advancement of the whole segment.
So the question remains, would he benefit from setting back his jaw angles.
To me, your questions resolve to demonstrations of using a faulty foundation to ask them and it's like trying to build on a foundation of sand to answer them. So, I leave you to your OWN observations. IF your observations are correct on what ever you use to base them on, you can use them to answer your own questions.