Are the landraces better suited because they are lighter? A lot of chickens in the US are probably too heavy to do very well because they can't bridge the snow and instead sink in it. I found a rooster high centered a couple years ago! Luckily he hadn't been there longThere are some breeds that do manage on deep snow; the Finnish Landrace and some of the Swedish landrace breeds for examples.
There are also local breeds in Afghanistan and Northern China that are reported to cope well in deep snow.
