You can hit with any gun while spraying. Some of them are pretty good to spray for longer than others (the M4 is one of these). The K121 is not. You will be incredibly more effective if you shoot it the way I mentioned.
Yes, the videos show how not to shoot the gun which is readily evident in the results that you saw. And yes, it’s a comparison as to how awful it is to shoot the k121 like that compared to something like the M4. But in reality you never shoot the K121 like that if you want consistent good results. Hell, you shouldn’t be shooting the M4 like that either. Your whole argument is based around shooting the K121 incorrectly and how much worse it is when shooting it incorrectly. Which, as you can see, doesn’t work very well.