That fact is becoming clear to those who study the subject, and it's why some agencies have converted to .45 from their .40's, to get real improvement, and why some have gone back to 9mm, and more are making plans to.
Most agencies choose based on budget, whatever meets the specs and is in budget is what gets bought.. Total fallacy that 45,40 and 9mm all have the same performance.
E-MCsquared - The force of the recoil = the force going forward
Are you telling me 9mm per same specs on a given gun recoils more than a 45??? Sorry no...
45 certainly can expand to a greater diameter, 40 and 9mm are closer in expansion. The main thing is accuracy is king and in general the diameter of the cavity is significant enough among all these rounds to produce the results needed for self defense.
Shoot whatever works for you, but 9mm is only king of self defense rounds if its what you like and choose to use, same for all the other rounds.