Let's put it this way as a comparative. Production Reds (which are often sold as Rhode Island Reds) are much, MUCH smaller in size than their true Rhode Island Red counterparts, yet the true Rhode Island Red is less productive than it's hatchery counterpart. The true Rhode Island Reds, which may have existed in hatcheries 20-25 years ago may have been more true to type and size than what is available nowadays. The reason for this, is that the birds are smaller as the breeders chose birds that were most productive as breeders. They wanted birds that reached maturity fast and produced as many eggs as possible to increase their sales. It's why the overall body shape and size of the breeders for a hatchery are so much smaller than you would see at a show. A bird at a show, as many have stated before, would not be used in a hatchery breeding scheme as they simply do not mature as fast, nor lay as many eggs as the more productive, and yes, smaller birds. By choosing these more productive birds, the smaller body frame caused the overall size of the bird to drop to little more of that than the Leghorn. When you compare the two side-by-side, a production Red (hatchery Rhode Island Red) and a Leghorn, the overall body shape and size has very little difference at all.
You could do the same with a Brahma. A production bred Brahma (really nothing more than a underfeathered Cochin with leakage...) is now developing the same smaller framed body style that has taken over the hatchery breeding scheme. A smaller bird simply matures faster which allows for more eggs to be laid in the bird's lifetime. Then there's the aspect that once the bird reaches maturity, it requires less feed to sustain it's own body mass so more of the nutrients are able to go into producing eggs, possibly at a faster time frame. A larger bird requires more feed to not only sustain it's larger mass, but to also maintain a body mass that is necessary to reach it's optimum level for reproduction.
Another example is the Leghorn. A production Leghorn is one of the best layers I've ever seen. A Leghorn from a hatchery or used in any production facility will have no issue outlaying a bird bred for the showroom or for the SOP. The reason? The body size of a production Leghorn is, overall, smaller than a bird bred towards the SOP. Truly the only things that a Leghorn from a hatchery can claim as possibly resembling it's breed description is that it's comb flops and it lays white eggs.
Nice to see you still lurking on here my friend! The Langshan was bred to be the more prolific egg layer of the Asiatic class. You won't find as much meat on them as you would a Brahma and well...the Cochin is nothing more than a fluffy pincushion! 
