What made you assume it will be 2x speed? It doesn't say how many they are hiring, or how many they have doing this job now. It could be anything from a 10% increase of work force to well over 1000%. So we have no idea how much this will improve their production speed, it's all merely guessing. Besides, graphic design (if indeed the translation is correct, last time I checked this ad was in Japanese) is usually about making 2-dimensional visuals, like logotypes and such. Sure, textures might be included as well (but I wouldn't call making textures "design") but for the speed of creating DLC packs, the modelling assistant is probably a lot more important. That's where I suspect the textures are created as well, if indeed the translation of "graphic design" is correct.
They do a good job, that's for sure. But better than PD? Not even close. Well, maybe they could do a good jobb improving some obsolete standard models, but not more than that. (Reading bout Sandrox makes it sound like they are rather copying models from other games and converting them to rFactor - that's hardly how it's done at PD. I also doubt it's legal...)
Also, those independent artists are hardly "like you and me". My guess is that they are highly skilled semi-professionals.