I think another aspect to consider is that a good developer who can effectively train and teach other developers on a team gets huge leverage on productivity. It's that leadership and teaching which creates a culture, and amplifies their own efforts through the sharing of knowledge, which then makes it possible to succeed wildly in a project. Looking at just their code might be less than stunning, but once you realize how much of their thought process and technique gets incorporated by others, the impact is huge. And that benefit goes to all of their co-workers' next employers and next projects.