Is there really 3x more silver in C41 than in B&W film? My impression was that with the final density being due to dyes no silver and the overall CI generally being lower, the quantity of silver was generally lower in C41 film. And that C41 fixer seems to be more-dilute than B&W fixer.
The silver has two functions in chromogenic films: light-sensitivity and image-forming. To a certain extent those functions must be kept apart.