Drawback to the pistol caliber is lack of penetration, especially if someone is using a vehicle for cover.
Pretty sure that'll be the case no matter what you use if they are doing it right (behind the block or wheels). One of the bonded 9mm will probably go through the plastic/ sheet metal on most cars today. But you're right that you are trading a few factors off to get the common mags/ammo, concealment and light weight.
My gut feel is that if you're in a 'get home' situation, slugging it out with someone who's taken cover isn't the best option. Personally I'd just be lobbing a few shots in their direction so they keep their heads down while I get out of Dodge and find another route.
I know you tend to train LE/military, where bugging out isn't an option...But for us civvies in a get-home scenario, the Monty Python plan of confusing them by running away more is always on the table.