Dual purpose, the label, is generally misunderstood. The label means that the laying hens have enough flesh to be useful after they are replaced. In that sense, most are. The desire was to have a good fowl for the table, and the spent layer to not be a waste product. This meant birds with more flesh, which also meant larger birds. Some of the larger breeds were never known for this for misc reasons. For example, Minorca. They are large enough, but the emphasis was the exceptionally large eggs. Certainly doesn't mean that there is not enough flesh on the hen to be useful though. The males take too long to fill out the extra large frame to ever be known as a meat bird.
Modern concepts of efficiency have proved this concept to be irrelevant, but it is still relevant to small flocks that do not fit modern standards for efficiency.
Contrary to our thinking the smaller more active birds are the most efficient birds for small farms. We do not keep large dual purpose fowl for their efficiency, but for our pleasure.
Modern fast maturing breeds have the most potential for some level of efficiency. Birds processed at the peak of their growth curve, that comes as early as possible, is the birds most efficiently processed. Raising birds to older ages, gets less and less efficient. This is the concept behind the modern broiler industry, started by birds like the new Hampshire and Delaware. That is part of the draw to the Catalana Delaware, and New Hampshire for me. I call the Catalana the "Spanish New Hampshire".
Other than European styled "fattening" fowl, the concept of raising chicken for meat is modern. The move to the cities at the turn of the century opened this market it up. Before fowl meat was a luxury for the wealthy or a seasonal treat for the peasant. Generally speaking.
I'm honestly not sure if you're agreeing, disagreeing or attempting to enlighten but you do, without fail, make me think.
Thank you
M