Exactly.I used to carry a Beretta .25. I think it held 7 or 8 rounds. I'm pretty sure I could kill someone with one. We used to practice by "lacing up". That is, first shot to the sternum, second shot 2" higher, and each additional shot 2" higher until all 8 rounds are spent. So in addition to the two shots to the sternum and 2 shots to the throat you'd get 2 or 3 to the head too.
Now a 9mm is not a .25, and it carries a lot more rounds (excellent for indiscriminate spraying all over the place), but for someone who practices and shoots well, it means a double tap to the vital area of the torso and a single tap to the head for a sure stop. A .45 will get this done with fewer shots. If you have only one assailant, then the 9mm will serve you well. But a .40, .45, .357, 10mm will end a fight with fewer rounds spent, and if you are facing multiple assailants that means you can switch targets quicker, and end the threat sooner.
I would take the .40, .357, .45 or the 10mm before I would consider a 9mm (oh, hey! The FBI agrees with me too!).