It's something that can't be "proven" one way or the other because some guys are just different/better/worse as starters compared to relievers. I fully wanted Chapman to be a starter for the Reds. But now that he's established himself as one of the game's elite closers, I'm sitting back and enjoying the ride. He just had one of the best seasons in MLB history and that's not even stretching it. Maybe the Reds' brass feels that his body wouldn't hold up as a starter with how hard he throws? I don't know. I just don't want to argue with what's clearly working.