I get that . But can't that be improved by improving your core strength and pliability . So if my core muscles are strong and flexible through exercises and with repeated practices , won't my throwing power improve? I know I am making it sound simplistic , but isn't that the case?
There is a reason why NFL GMs look for guys with big arms. Right or wrong - they understand that throwing is an athletic event. And while certainly people can improve their athleticism - there is a limit that depends on your frame and genetics and so on. For example Tom Brady claims to have taken 0.1 seconds off his 40 yard dash. But he can train forever and he will never run a 4.3.
It really depends on your potential and your current ability. Going with a weight lifting comparison - most men with training could likely bench 300lbs. But the guy benching 400lbs - he might be already beyond your potential - even if you put everything into it.
So going back to Mac - he fell because he didn't have the best arm. Now if everyone thought he did have the potential to have a huge arm just with some training - he would not have fallen. Basically the Patriots are saying - this Mac Jones guy I think we can coach him up enough to be an excellent QB. Other teams are saying - even if we coaching him up - his arm is to weak. Let's pass on him.
Who will be right? We will find out. My point is its not some 'likely scenario" that Mac Jones will greatly improve his arm strength. It would be unusual.
I will say that I think modern coaches in baseball have gotten really good at squeezing out throwing potential.
When I was a kid almost no one threw 100MPH. Nowadays seems like they have dozens of guys who can hit that kind of velocity. That's because baseball coaching has gotten much better. They know how to analyze the throwing motion - what muscles to strengthen and stretch and how to work on the kinetic chain for maximal velocity. So now it seems like a big tall kids can hit 100mph - where in the old days some weakness might have kept them in the low 90s.
Mac Jones has a small frame and normal length arms - so not sure he can ever be a guy with a cannon. But heres to hoping the Patriots got it right and those other guys got it wrong.