While the extreme "master of one" exists, most academics I know have cross-cutting interests.

We also shouldn't forget that the vast majority of politicians today are lawyers by education. To whatever degree your assumption holds, it is true of the status quo today as well. Even in that case, having a more diverse set of "masters of one" would be an improvement.

Slight correction (can't edit): law education is most common for politicians in Western countries, but not the majority.

For the US, 32% of the house and 47% of the senate holds a law degree.