I recall reading about the other important shovel innovation: reducing the size of the scoop; with smaller scoops, shovelers moved more earth overall, because they became less fatigued.
I hate to bring bad news, because obviously your mysterious 5000-year project is near-and-dear to you: Jesus will be returning soon, and one millennium thereafter we will have a new earth. So, unless those 5,000 years look backward....
Frederick Winslow Taylor determined that the most effective load was 21½ pounds, and found or designed shovels that for each material would scoop up that amount. He was generally unsuccessful in getting his concepts applied, and was dismissed from Bethlehem Iron Company/Bethlehem Steel Company.
Nevertheless, Taylor was able to convince workers who used shovels and whose compensation was tied to how much they produced to adopt his advice about the optimum way to shovel by breaking the movements down into their component elements and recommending better ways to perform these movements.
It was largely through his disciples' efforts (most notably Henry Gantt's) that industry came to implement his ideas. Moreover, the book he wrote after parting company with the Bethlehem company, Shop Management, sold well.