I'll keep it brief and general, but that assumes you are pulling the trigger at your maximum cyclical rate. I do see this. People panic and fire as quick as they can until slide lock, sometimes after the first bullet did the job and sometimes for a lot of missing. I would counter with if the first quick hits didn't get the job done, it's time to slow down and start getting better hits. Easier said than done, of course, but it's where realistic training and stress inoculation come into play. Personality may come into it as well, the reason that two cops side by side on a stair well with equal views and equal circumstances may result in one guy firing 2 and one guy firing 9. There are folks out there who've ran through every mag they carry on more than one encounter, and guys who've gotten in done in three or less every time. That is NOT to say that one is without a doubt better than the other, different circumstances, distances, etc....however I tend to listen more to the guys who've gotten it done in fewer rounds.
There is certainly nothing wrong with more capacity, assuming you shoot it equally well...but bullets are bullets and time is time. Both need to be managed in their own way.