450 grams for the R470 is for the rims alone.

https://www.dtswiss.com/en/products/...durance/r-470/

The weight spec for Roval is for a complete set with hubs and spokes.

https://rovalcomponents.com/products...disc-wheelset#

I'm no expert, but I don't think carbon wheels are necessarily lighter than alu. They're just able to be made deeper without adding weight.