agreed, there is no formal standard for the SFH. BUT, there are certain requirements of the SFH that have to be met, in order for the bird to BE a SFH... and in order to keep the breed viable, some choices have to be made, ESPECIALLY since we have such a small gene pool...
yes, over the last 500 years the sfh has evolved into what it is, but less than 50 years ago, it was nearly extinct. so since then people have been working to restore it, and making selections to continue the breed's survival. they may not be selections for anything obvious to anyone but the person breeding them, but it's doubtful they let all roosters live with all the hens and never ate one of them... and as such, that is 'breeding' not natural selection.
as far as split wing, it is considered a fault in every recognized breed. it is also present in nearly every breed I've ever encountered. some more so than others. with such a limited gene pool, yes the split wing seems to be more common, but it's still a fault. just as having a sfh that has no mottling, or a pea comb or rose comb would be considered a fault.
every breed has evolved through a series of selections, whether consciously made or not...
what we (as a group of sfh breeders) have come to a consensus with, is a series of things the sfh IS, and things it isn't...
Hens weigh 4-4.5 poounds, cocks 5-6 pounds.
They have a medium sized single comb, which may be wavy in crested birds. Wattles are well developed.
The eyes are orange to red and round.
Legs are yellow. On some darker colored birds, the legs may be dusky or mottled, but the bottoms of their feet should still be yellow.
They may be crested or uncrested, but the crest should not be overly large so as to impair vision from above or behind.
The roosters have a nicely rounded breast and upright stance (some describe it as 'proud'). Hens also have a nicely rounded breast but a more horizontal stance typically. Tails on both sexes should be raised above the level of the back and well spread. (pinched tails indicate a narrow frame, poor laying ability and smaller eggs)
The base coloration of the birds will vary, including red, orange, brown, black, blue and yellow.
Both sexes will display varying degrees of mottling (ie the flowers they are known for).
Things considered faults would be split wing (missing the first or axial flight feather), side sprigs on the comb, wry tail or dropped tail... if the only sfh you have has faults, I would say use it until you can replace it with something better. yes they are faults, yes they are insidious and stick around for generations, but they can be worked with if the bird is otherwise exceptional. if it's got more than one fault, I'd say pass on by and find another bird, personally.