On the smaller turbines I worked on, the speed of rotation was controlled by feathering the blades as you’d expect. Braking was also achieved the same way, with the friction brake acting as a “handbrake” once the blades were slow enough.

One thing that some people don’t consider is that the direction the turbine faces is also controllable and therefore used for braking. A lot of people think the turbine is blown by the wind to face the correct direction, but there is a separate wind direction sensor and a motor to turn the turbine.

The friction brake could be applied at speed, but that was for emergencies.

There is so much power in the wind. If you are a little late with feathering you might end up having too much momentum to be able to use a friction brake without burning it up. So a long period of steady wind followed immediately by an increase to the point where you can no longer stop the machine is quite risky: all that stands between you and certain destruction is either a lucky lull in the wind or your continued ability to feather it and that can get surprisingly hard when you are dealing with high winds. To the point that if you go 'coarse' at high RPM you end up pulling over the tower due to the extremely long arm for that force to take effect.

Never ever underestimate what the wind can do. Wind turbines will always have some latent risk (as do most other activities and constructs). For every design there is a pathological set of circumstances that should never happen. But once in a long while it does. What should surprise you is that so few of these accidents happen that they are news.