If you have both hands at your keyboard, that's 100% true. However, it really works well with workflows which rely on mouse, stylus, touch, or controller input.
Especially when used for "creative" or "artistic" tasks (e.g. painting, video editing, 3D modelling, etc.) pie menus can really have a benefit because you have your hand at the stylus or at the mouse most of the time anyways.
Especially when used for "creative" or "artistic" tasks (e.g. painting, video editing, 3D modelling, etc.) pie menus can really have a benefit because you have your hand at the stylus or at the mouse most of the time anyways.