OP did you watch the video ? Red cone movement is out of phase to the input and 100% distortion....
It’s not just about bass, one needs to consider the source the root causal reason for higher output.
one form of higher output is achieved with a mechanical device to focus energy - imo at cost to fidelity. Horns are not everyone cup of tea. Since to appear focused on dynamic drivers, I will comment more about those..
for dynamic driver speakers, non pistonic motion creates higher output thru constructive and destructive interference. Check out the Utube video on the comparison of two 5” midrange, for a dramatic and easy to understand visual representation of in and out of phase behavior. That video is linked on the Vandersteen website. For a non pistonic driver ( most of them frankly ) A great deal of output is just in and out of phase trash. When a pistonic cone assy is fitted to the driver with equal mass, output drops. The bottom line is trash counts in the efficiency measures. Another reason to listen and not get too wrapped up in less than critical specification. Pay attention to impulse response tho!