P.S. In terms of raw cool-factor, it's hard to beat this: https://www.youtube.com/watch?v=3tEYcUSQDyw
I won't spoil it by describing it.
An example of what (a world record holder) can do with a revolver.
But if you're swamped with zombies, then maybe simply having more firepower is an advantage.
Single button magazine ejection, slam your Uzis down onto fresh 100 round magazines. Bonus points for an automated system that moves the next set of magazines into the perfect arms length position at your side for the next reload.
Two handed reloads are for chumps when you are fighting zombies. You would be the guy I'm standing behind to give me that extra few seconds while they're busy eating you. That way once I finish off your attackers I can pick up your freshly loaded (but unspent) gun. And triple-wield!!
The other advantage of using two guns is you get to let one cool down while reloading the other which helps avoid melting the barrel. This eventually ends up with a Gatling gun. Which is arguably hexa-wielding.
What do we actually want to create with our games? Complete lack of realism can be fun (e.g. surgeon simulator), and these games are proliferating. Games with more realism may be able to create more meaning and insight for their audience.
It also speaks to the absurdity of FPSes. I was laughing so hard at all the little FPS tropes. Like how the guns were cached in "obvious" places or how the guy knew there would be something of use inside the conspicuous pot outside.
"Okay, now dual-wield the pistols." --said no one ever in real life