Earlier quoted context omitted.
Concerning over-penetration, that's largely a function of ammunition. Hollow-point rounds from a submachine gun don't (practically speaking) over-penetrate any more than those fired from a handgun.
If the concern is hitting something behind your target that you're not supposed to, over-penetration would actually be pretty low on my list of concerns about a submachine gun.
Are you suggesting that submachine guns make you more likely to miss your mark? If so, this is spoken like someone with absolutely zero firearms experience, as submachine guns are much more accurate and controllable than handguns...