I would argue that it isn't actually luck, it is variance. When you get enough of a sample you finally get to see the skill without the variance getting in the way. Of course these samples are pretty huge. People always fail to recognize that even half a season isn't really a very large sample when you are talking about how good a player is, heck a full season isn't really a very good sample, that is why people use the 3 year averages etc so much. I have a friend who plays poker for a living, he has made hundreds of thousands of dollars with it now so is obviously a skilled player. He still sometimes goes months at a time where he loses money over huge samples of hands. Baseball is no different, so much of what happens is out of the individuals hands it takes a long time to get a really good idea how good someone is.