I disagree. I think when someone with the requisite physical talent realizes that he's overmatched, he's likely to figure out what it is he needs to do to stop being overmatched. Now, that doesn't mean the Reds shouldn't change things up for him so that he now has a chance to have some success after tasting adversity for what is probably the first time in his life. Clearly, this isn't working, and it's probably not going to correct on its own. So perhaps they schedule him to throw only an inning or two out of the bullpen every four or five days until he has enough success/confidence to go back into a starting role. But I don't think there's any reason yet to believe this year is somehow being wasted or that he's not still on the path to being a quality big leaguer.
It DOES, however, provide an answer to people who were whispering that maybe he was going to be the next Doc Gooden or Jose Fernandez at 19 or 20 years old. Including, just maybe, Greene himself.