Not all crews went on all runs, maybe about 10, and I doubt that Sadeas would have gotten half of them. Maybe a third, but even that seems unrealistic. So that's 525,000x(2/3)/4 = 87500 bridgemen losses for Sadeas. Also, Sadeas was one of the more callous highprinces sin terms of bridgemen lives. It goes to both extremes. Sadeas, with huge losses in bridges, and Sebarial and Dalinar, with little to no losses.
And sniped by King of Nowhere. Considering both of our points, losses are nowhere near 5,000,000. Math corrected!