To put the recent research of small flock Delawares into perspective, the broiler study used birds from a hatchery, the layer study was funded by Purina (I think ... I'll have to check). From what Delaware breeders believe, the hatchery Delawares don't much resemble the standard for the breed, and I believe they are a mix of breeds including industrial layers and such. Perhaps for those Delawares, and any hatchery-sourced "Heritage" breed, the industrial research is more applicable than it is for old lines of show birds and such.
For someone a few generations into a breeding program, the birds would maybe not resemble industrial birds in many relevant respects. The birds will become increasingly localized with each generation.
There has been some anecdotal study of working with non-industrial Dual Purpose birds ... Buckeyes, actually ... through the Livestock Conservancy. They suggest a specific feeding regimen. Also, there are some other "networks" that exist to promote small flock poultry operations that offer flock certification, help choosing breeders, and instruction about feeding and caring for birds on pasture. Maybe we'll start getting more substantial real-world info from them.
But for now, if I want to know about differences in protein sources in poultry diets, it's the industrial research that has the most info.