Ornamental breeds may be less needy because they likely will not lay many days a week. Smaller/thinner birds won't need as many calories as say, an orpington. Less feathers = less protien needed to grow them.
They will have health issues if they only get a bit of scratch each day. The birds today have more taxing done on their bodies than the birds back then.
They likely will lay less, may have weaker immune systems and lower fertility and younger deaths