If we even forget about online/offline aspect, I am not aware of any data that is available on traffic conditions and covering large fractions of the world. By just monitoring your current speed and comparing it to the speed limit, I cannot make a choice of the future road since I don't have any data to base it on.

Actually, the best offline selector in this case is you - as a driver. You see traffic ahead and can decide to either stay or turn. If you turn, Valhalla will reroute accordingly. And again, you could alter your path as well.