Carbon is not always lighter than alloy.
Take Ritchey WCS kit for example. The carbon stuff is slightly lighter (like 10-20g) but it's not as stiff as the alloy stuff. Oh and alloy WCS is half the price of carbon WCS.
Just because it's carbon, doesn't make it better. Like any material, the higher end stuff is the dogs danglies. The lower end stuff might not be better than similar priced stuff in other materials.