I agree that many pitching coaches are Advertising with velocity gains of teenage Players who would have gained velocity throwing a coconut. for a lowly trained or Young Person almost any Training will provide gains and kyle will be the first to admit that.
once you reach a certain Level genetics start to Play a huge role.
however even at the highest Level there can be gains. kyle Trains many pro pitchers and a lot of them have gained even if it is only 2-3 mph. also even at the mlb Level until a couple years not a lot of science was used, although that is rapidly changing, many things just were accepted as true.
but I agree there are many Money grabbing programs out there, you often read something like gain 12 mph in 6 weeks or so and of course that is BS.