Right. There is undoubtedly luck and non-pitcher factors at play. But I can't believe that that is all of it.
R. A. Dickey is a great example of that. Days where he has a crazy amount of action on his knuckeball , in addition to striking more out, many balls made contact with are weak dribblers and popups. When he has a bad day and they're not moving like he wants, he gets hit hard with line drives and long fly balls. No one can convince me that how he's throwing has a negligible impact on the result of that game, and that luck is the difference.