It cuts the other way too. I could just as easily say it rules out egg size/weight as a possible benefit of keeping the birds cooped with a large feed supply, as the eggs don't come out any heavier with commercial feed than with free forage. It depends on how a person wants to spin it.Not sure that egg size is a significant measurement, but at least you appear to have some evidence that it can be ruled it out as a possible benefit of free ranging. What would definitely be good measurements are analysis of the nutrients in the yolk (harder for the average person to do) and successful hatch rate (would be an interesting comparison).
I can definitely taste the difference between my free range eggs and cooped eggs and see a difference in yolk coloration. Does that mean free range eggs are more nutritious? I don't know.