Yes, many other breeders of show quality exhibition birds report that a separate male and female line are necessary to get the best birds. I raise several other breeds and I know many very serious breeders of one or two breeds will have two lines. I have a couple of issues with this breeding philosophy. First, it requires more room and essentially cuts in half the number of breeds you can work with if you maintain separate male and separate female lines for each. I like variety so this is hard for me to to do. The second issue is that from a sustainable agriculture aspect and a heritage breed aspect I don't like the fact that in order to raise a breed of chickens you have to have two lines to breed chickens that meet a standard. Shouldn't a breed of chicken be able to be bred In a 'normal' fashion?
I have the same issue with breeds that are now requiring the use of artificial insemination to get quality birds. Breeds of dogs, like English Bulldogs require artificial insemination and I think this is unnatural. I am very capable of AI ing birds and will when necessary for other reasons, but not to maintain a breed to meet the standard.
Ok, of this particular soapbox. Nothing wrong with having sex separate lines, just not a method I want to use, I will give it a shot with one line and heavy selection.