Keyboard mouse is really the worse setup, technically. If we remove player skill from the equation it would go like this:

Full Keyboard
Controller
Keyboard+Mouse

Imo full keyboard is clearly the absolute best because everything is in one place. Additionally, it has greater potential for customization because there are a LOT more keys to bind. Everyone knows how effortless it is to type with a keyboard; playing a game with a keyboard is basically the same thing. It does take a lot of getting used to..like remembering what is binded where and getting used to "typing" in that language. But once you do there is nothing more efficient.

Controller is basically like keyboard with less buttons to bind. But really that is only a very small knock against it. You could argue its equal to keyboard, but I still give the edge to keyboard because of its full functionality and greater customization. As has been said, you can't type with most controllers..although some controllers do have a keyboard. Whether a controller is better than a full keyboard will depend largely on the game's control scheme and how keyboard bind friendly it is.

The worst option is a keyboard+mouse. It cuts the keyboard essentially in half, giving you few keys to bind, and leaving a lot of skills out of reach. Clicking skills takes too long, clicking to target is not reliable. Most casual gamers will obviously be more comfortable with the "point and click" setup, but as at technical instrument it is definitely inferior. I don't really see how we can argue its not.

Naturally player skill makes up for all these things, but there's no way a keyboard/mouse is technically more efficient.