It is a nice graph. But, these are differences that most people will never really get to evaluate. There are more variables than simply moving mass at play. Motor Strength, inductance, suspension compliance, air spring (or not), etc.
Comparing a light moving mass, higher Fs, high sensitivity driver to a heavier moving mass, lower Fs, lower sensitivity driver is just not a good apples/apples. They are designed for different things. One is designed for more output at higher frequencies for a given input signal. The other is designed to be able to generate more output for a given inout signal at lower frequencies. Even this comparison is waayy too simplified.
For more info on the subject, you need to pick through some of this:http://www.baudline.com/erik/bass/thomas_danley.html
Or read what Mark said above.
I tell folks the following:
If you do not have near identical clean (read: low distortion, however you want to measure it, but a baseline must be set, whatever it is) output and extension with flat frequency response, you cannot really compare two alignments with regards to group delay, transient response, etc. without significant bias. This means that in a small room, the 2 compared speakers must be in the exact same location when being compared, as differing locations could lead to differing freq responses. Especially in small rooms. Outdoors, not so much.
I don't know of too many folks who have compared 2 LF (or fullrange, or whatever) units that have fulfilled the above criteria.
Also, there's what I call the 'paraxial criteria' of audio. The less the driver has to move, the more accurate the reproduction of the signal, just like in optics, the closer you are to the optical axis, the lower the aberrations. Very large Xmax drivers may be great for spl, but not necessarily for 'starting and stopping on a dime' like a 2226H.... Then again, not apples/apples, and different freq ranges with differing excursion needs, and......you can go round and round on this topic. Just too many variables. In general, spread the load (be it with a horn/waveguide or multiples) and don't make a driver work too hard...