NO, not always. When VIN is close to VOUT, a linear may be as efficient or more efficient because the PWM switch transistor will be ON most of the time and it will also have switching losses added on to the saturation conduction losses. In high current apps like 25A load, switching losses are VERY HIGH. With 25A load, the losses in the catch diode are also very high. The belief that PWM is always more efficient than linear is simply not true: when VIN gets close to VOUT, switchers lose their advantage.