You ought to clearly ask the question you want to ask, not other broader questions. If I totally missed a context that should have been clear it was likely because I was skimming a lot of the trite semantic based back and forth, and you have my apologies. To answer your newly clarified question, defeat armor. For many civilians in the US there are legal prohibitions on AP handgun ammo so even soft armor will defeat the legal bullets coming out of a pistol caliber. Of course there is hard armor that will defeat pistol rounds while other rifle rounds will pass through. Another answer would be have a bullet construction that offers reasonably reliable terminal ballistics (say can meet FBI standards) while simultaneously mitigating over penetration. The rifle can also offer vastly superior terminal ballistics (particular if one is limited by the strictures of international law to not use ammunition that expands or flattens easily). A serious increase in terminal ballistics is kind of a big deal when you are shooting people who present a threat to you. Why do you think so many professionals are moving from sub guns to things like the MK18 or similar style/configuration of weapons. Now, a lot of bad guys have moved on to a better place grace a various sub guns. Certainly a pistol caliber gun is a pretty formidable weapon inside of 150 yards or so. It simply does not have all the capabilities of rifle rounds though.
I've tried to discuss the issues as relating to various situations. It would be easy to say, no combat for a civie, or LEO, or military, and the discussion will change. Its hard to hit between the goal posts when one keeps moving them.