The issue is training and the limitation of the firearm. For example pistols I would consider ineffective at any distance beyond 25m without a significant amount of training, due to the short sight radius and the fact the firearm is held out from your body. You add a shoulder stock to the same pistol and I would increase the effective range significantly, to around 100m (provided the sights are set up for it). One thing with the one hand pistol stance at 50m, is sure you can do it effectively at the range when no one is firing back at you, but once it is a real two way range, you won't have the time to line up and make such effective shots (without a significant amount of training).

One thing with that how far will a 9mm kill video is that the ammo he is using isn't standard FMJ ball ammo. With the standard ammo the ammunition used does become less effective the farther you get.