As the OP here, let me invite you and others here to address the actual idea of whether coaches are useful in professional sports, instead of hijacking things with your little arguments. If you guys want to just insult each other take it somewhere else or start your own thread.
This idea that he can't change his mechanics is nonsense. He can if he wants to. Throwing is throwing, and MLB pitchers ten years older than Fitz have reworked their mechanics. Every guy coming back from Tommy John surgery has to relearn his mechanics after the surgery. The "old dog"- "new tricks" maxim doesn't hold for things that are more skill than athleticism like throwing. Ditto for a golf swing, tennis swing, hitting a baseball... Skills that are taught can be learned at any age. How many golfers have reworked their swing using a swing coach? Virtually every single one. The mechanics of throwing are a skill that can learned. It's just muscle memory. Anything can be learned at any age if the pupil is commited to it.