… of the beholder.
In other words no two people see the same thing. And what usually happens in these situations (asking for advice on the Internet) is a variety of opinions are posted and you must choose what you think makes sense. And what makes sense is what you’re most familiar with (are already predisposed to) and becomes a “circular” exercise.
That being said…
Your son, overall, has the basic throwing elements to build on ( 95% of the players I see do not have this foundation).
With respect to trying to give advice for improvement is virtually impossible to obtain anything meaningful from these postings (no offense intended to those who post it simply been my experience). And by meaningful I mean something that your son can translate into actual physical changes to his delivery.
What has been most successful for me in my attempts to help players Is a 4-step process.
First is to first ask them what high-level player (major-league) do they try to emulate? And if I agree with them I then begin a process of doing a side-by-side comparison of the player with their major-league counterpart.
this is extremely important because unless they have a visual image of what they need to look like (or think they should look like) it’s virtually impossible for them to initiate meaningful changes (my opinion).
So I would be curious as to who your son thinks he looks like ( major-league counterpart throwing wise).
Second is the analysis.
I have taken a quick look at some of his clips ( converted them to AVI and then looked at them frame by frame) and do have some “observations” which if I have time and based upon your response to my question regarding his emulation, I would be happy to share (again as time permits).
Third are the formulation of “cues” which can be used to initiate changes in mechanics determined by the video analysis.
And fourth is a continual process of going back to step number two (video analysis), comparing to see if changes are being made and then repeating the whole process over and over again.