I like this analysis and a large part of this argument from each side seems to supports it.
I have no doubt pitching coaches do have an impact on the team, but the pitcher also has to be willing to listen..... And I agree that money and agents probably have an impact in the way that some guys feel they really don't need to listen.
When pitchers like Halladay, Lee, Carpenter and Lohse are mentioned it seems that they were all guys willing to listen, and Duncan was in a position to gain these guys attention as well..... In turn they did end up listening and look what happened.
I also think the Curt Young argument also seems to sort of support this. From what I saw on TV and at games, which is of course limited to what you can see with your eyes, he was out on the mound less than any pitching coach I've seen in Boston. This very well could be because our pitchers didn't really listen to him. He could also have more success in Oakland because they're almost always young pitchers coming up through the system for the first time, which likely would have them more willing to listen. Of course, this is totally hypothetical but it makes sense.
At the end of the day, it does seem that the money people make in baseball now and the way that contracts and other things on the more bureaucratic side of the game work entitle some players to not listen and really not catch any flak for not listening.