Glock is negligent in their faulty labeling. A correct holster is absolutely critical to bring a Glock handgun up to the level of safety of other handguns and the holster needs to be considered part of the firearm itself. One would never cock a revolver and put it in their holster (or waistband gangsta style) yet that's exactly what they do every time after they chamber the first round in a Glock.
I agree with your statement about a correct holster being critical, but no one at Glock or anywhere else I was aware of has suggested wearing a Glock without a holster ‘gangster style’ or otherwise. Not sure what faulty labeling you mean.