I recently tried to convince our HC to use Juggs machine to better develop our hitters. However, I think your son's coach is making a mistake if that is all he is doing to prepare them for hitting in game situations. It is a tool and should be treated as such. A good program is going to incorporate tee, soft toss, coach-pitch BP, and a machine. They are all valuable and provide opportunities for hitters to focus in different ways.
Our HC has not incorporated machine yet but maybe that is why our guys struggle against velo!