For wind turbines with a high tip speed ratio you'll got an optimum in one design point. So he got another shape of rotorblades at lower local tip speed ratios. So you can calculate this, what was build for many centuries. He developed a diagram for the maximum efficiency for HAWTs depending of the the design tip speed ratio, the number of blades and the lift to drag ratio of the profiles. Measurements gave nearly the same values.
Some people build all things with a round leading edge and a sharp trailing edge.
It is a simple method and works very fast. The momentum theory and the wing theory must give the same forces. The angle of attack will be modified until the forces are equal. All people don't believe in the results of the blade element method, but everybody use it. People like me want to calculate better, but it's not easy.