I have a no disagreement at all with your thoughts other than your limiting the problem to food / environmental only. I remember a WDFW hatchery guy listening to the argument but it was about Coho size. I still remember his terse response. How do you start with a 10 to 12 lb average brood and get to a 5 to 7 lb fish. Net the hell out of them with a mesh size that allow smaller adults to escape for generations resulting a higher portion of small fish in the gene pool and hatchery eggtake. A fish and cow are very different but all creatures can be modified by altering natural selection be by natural conditions or those inflicted by humans. In the end I imagine it is a combination of both sides of this coin.