Sadly it seems that a lot of dual purpose birds are in fact no purpose birds, neither decent egg layers or good meat producers. It's great that there are some who are breeding with production in mind, and those strains are invaluable, worth their weight in gold IMO.
Is it that our standards have shifted? Or our breeds have deteriorated? Deteriorated by hatchery productivity practices, or breeding the annoying productivity out of them to enhance their show potential? Or were they just never any good?
I think the only way we can even assess their potential is to work on them. I do think there is some purpose in genetic distinction and diversity.