I seem to remember reading something similar when British police started being routinely armed at airports twenty years ago, there was much ado about the sight of policemen strolling around Heathrow with Heckler & Koch submachine guns (or assault rifles, I’m not a gun owner so I don’t know the exact description of the weapons).
Someone pointed out that in the wide open spaces of airport concourses with their marble and glass fixtures the cops would pose more of a threat than any terrorist if they opened fire with those weapons as the rounds would be sprayed everywhere and ricochet all over the place. What was required in such an environment was a pistol or revolver firing aimed single shots with soft point ammo (again I stress I’m no expert) to take out the bad guy(s) but the cops preferred the “macho” look of the H&K’s.
I would think the level of over-penetration risk would be as much a function of the ammunition as the style of weapon. Higher velocity does not always translate to increased penetration. Further, I would think accuracy would be key to minimizing danger to bystanders. If guards can shoot a rifle or carbine more accurately than a pistol, I would think that would be a good thing.
Of course, I have no idea whether ammunition was chosen wisely.
MP5’s fire pistol rounds. Hence the “sub-” in submachinegun.