yea I would agree although I dont have a lot of experience with it.From what I understand the way genetics was explained by one BYCer, Blue is a difficult color to breed for hardiness -- even in the dog-breeding world they have problems. I lost my Blue Breda hen last year to heat-related complications and rather suddenly so I'm really closely monitoring these new Blue Breda juvies. Stress of shipping took its toll on them so I have them on electrolytes, chick probiotics, and Corid, while waiting on poop sample results from my vet.
Like any rare color you have to inbreed (or linebreed) to lock in the traits... This is probably where the lack of vigor come from.