I prefer 9mm for two reasons: First, the stopping power of 9mm +p 124g JHP is not much less than a .40. Second, the cost of 9mm is 25% to 50% less than .40, which means more time at the range, more practice, improved shooting skills, and better shot placement, which is the most important factor in self-defense.
Totally agree with you on shot placement, even a .22LR between the running lights will drop a bad guy. I just like the little extra stopping power of a .40 or .45. That’s all I’m saying