Incorrect. Efficiency is how well your body generates the power. The same power moves your bike forward regardless of how efficiently you generate it. It is just like buying bike components. The most efficient thing to do would be to buy the components that offer the best value for their cost. Or performance for their cost if that is your objective. However, after a certain point you reach the diminishing point and the cost becomes much higher for additional gains. Also think of standing while climbing. Standing is generally regarded as less efficient, in that it takes more "effort" to generate the same power. However, you can usually generate more power standing. In the case of a sprint, you are using more of your body to generate more power, but this has a cost and you will not be able to maintain it for very long. Aerobic vs. Anaerobic is not relevant. You would find the same thing if you got out of the saddle and "sprinted" rocking the whole bike side to side even if you were not at an anaerobic effort--that you just can't maintain that as long as you could if you sat down and spun smoothly at the same level of effort.