One can't fire 2.45 rounds of 9mm; on average that is 3 rounds to incapacitate an attacker, if given a "better than average cop" hit rate of 50% it is not unreasonable to consider that it could take 6 rounds (3 hits to stop, 3 misses) just one attacker. It is also not unreasonable that a citizen could face two attackers, based on averages a single stack might be at slidelock before both attackers are stopped.
A similar bit of reasoning led me to switch from a revolver to a semi a few years back. It used to be that capacity was one of the most-cited advantages of a pistol over a revolver. Nowadays the trend is to smaller and smaller pistols and, depending on the pistol selection, the gap can be narrowed quite a bit. Not that I am trying to sermonize at anyone, because I have a pocket pistol that I carry, too, albeit only at times when IWB carry is problematic.
Interesting discussion, though, I have to say.