I’ve heard that in a typical police firefight, something like 80% of all shots miss their target; out of that 17 rounds from your service pistol, you might get 3 on target.
I believe there’s even some Youtube videos of an officer and a suspect trading 30 rounds at a distance of 10 feet - and neither was hit.
High capacity firearms aren’t needed because a 9mm isn’t a sufficient caliber, it’s because most of your shots will completely miss - so you need a much higher capacity to begin with.
George Adamson of ‘Born Free’ fame (http://en.wikipedia.org/wiki/George_Adamson) was asked how to shoot a charging lion.
“Wait until he’s within 10 feet.” Adamson replied. “Don’t miss.”
If you have the nerve, caliber concerns become less important...