There are methods of tumbling Bitcoin (a la coinjoin) where every tumbling round effectively divides the confidence in a sender/receiver relationship by the num

There are methods of tumbling Bitcoin (a la coinjoin) where every tumbling round effectively divides the confidence in a sender/receiver relationship by the number of people participating in the tumble. So no, such mechanisms are not traceable by any reasonable metric. You're right about the volume of plausibly tumble-able money being low, but it's at least in the five or six digits per day.