Great idea for a discussion !
As t happens, I am moving directly into this direction, in other words, downsizing & only keeping functionality.
What we value after removing the 'show' from the operation here, is functionality.
Functionality is what has always dictated what breeds have survived the years, and which have been "kicked to the curb" so to speak.
Foundation, heritage breeds have not always been so functional, with more broodiness and less lay especially during winter months, these breeds took more time, work & feed and produced less meat & eggs than alot of other breeds did.
On farms, the RIR, barred Rocks and foundation Orpingtons did the work, feeding the Pioneer homesteders.
I guess "designer" chickens really did not come along until a ways after the depression...who could afford to keep chickens that just did not produce ?
The breeds I keep now that we are downsizing will be the breeds that continue to lay though the winter months, and go brrody less often, they must eat less and take up less space.
These will make less work for me & my bad back.
I suspect at this point, that will be my Marans.
Period.
The Blue Coppers and Silver Cuckoos are still, the best layers year round, that I have had, excpet for a great flock of Barred Rocks I had eons ago.
I look at everything about the bird: egg size, amount of lay, health, temperment, intelligence & 'flightiness' and Marans win.