I don't think the processor was over-engineered. I think it was engineered for the Mac, and the Pro was just a test-bed and "top-secret" developer testing tool.
But, yes, the software doesn't feel finished. Oddly, it felt more "finished" with the first iPad than it does now. The closer the iPad gets in feature set to the Mac, the less finished it feels. When there was a much wider divide, the iPad seemed like a device with a sense of purpose. Now—with the Pro models at least—it feels like a solution looking for a problem.