These are no perfect chickens. I started working with Legbar in 2011 and my mentor was a lady in the UK that had been breeding a really good line of Cream Legbars for 6 years that she got from another breeder that had been breeding the line for 6 years before it was passed to her. She told me that every year she would pull out the breed standard and read it with her birds in front of her to try to see what area her birds need to be improved. She said that with each passing year she became more and more convinced that she had never seen a Legbar that meets the breed standard and never would. So...while there are not perfect chickens then are some Cream Legbars that are pretty good and the Rees line produces a lot of them.
So why doesn't the Rees Line meet the breed standard? Well A few things to consider are 1) the Breed standard calls for moderately long legs. Many people have noted that the Rees line tends to have dumpy legs which are moderately short rather than moderately long. 2) The British standard list a twisted comb on the cockerel and a serious defect. The Rees line was developed to produce Show Quality pullets and Hens to the detriment of the show qualities of the cockerels and cocks. When Jill Rees started to show Cream Legbars in the UK after 4 years of breeding her pullets and hens were winning national championships but she was not showing any males. Her line was producing males that had twisted combs. After winning the top awards with her hens for a few years she did start to work on her males and has since produced some winning males too but the import of her line to the USA was before she produced any winning males and the USA Rees line still struggles with twisted combs on the males. 3) While not incorrect per the breed standard the Ree line in the USA is reported to produce greener eggs than many desire. The British standard list blue, green, or olive eggs for the Cream Legbar but sentiment of breeders in the USA is that a blue egg is the high quality for the Cream Legbar Green eggs are something that should be worked away from and olive eggs should only be produced by Isbars and are a culling point in the Cream Legbar. Production is also a consideration. Other lines may be more prolific than the Rees line (or less prolific depending on their breeding). Everyone has their own preferences for the breed so some love the Rees line. Some don't.
So...those are a few things to thing about. Every line of Cream Legbars has something "wrong" with it. The Rees line was imported because it was a huge improvement over earlier lines that were imported. It takes 3-5 years for breeders to create though own reliable breeding lines so many breeders that had been working with and improving the earlier lines for 3+ years when the Rees line was imported were not interested in it because they felt they would have to start over with their breeding if they brought outside blood into their flock. Other that had older flocks when the Rees line was imported used it to address weaknesses in their flock.
