Have one person do nothing but estimate the difficulty of a case(and be tracked and judged for the quality of their estimates), and the surgeon be tracked and j

Have one person do nothing but estimate the difficulty of a case(and be tracked and judged for the quality of their estimates), and the surgeon be tracked and judged on the relative performance given the difficulty. Then you could make a career out of doing well on difficult cases, or out of doing better-than-average on easy cases, and either would be viable.