People have taken multiple and lethal hits without vests, and continued to return fire, often without the knowledge they were even hit at all. What makes you think that hits to a vest, are going to cause someone hit, to cease any sooner? Especially since youre not getting any penetration into the vitals.
There is one true "kill switch" on the human body. It resides at the base of the skull, along a plane that bisects the little bump under your nose, and its generally accepted, that a hit anywhere in that triangle formed by the eyes down to that point, will accomplish the same result. As I said, if youre close, why bother with a body shot, if you can solve the problem much quicker, by unloading into the head.
If you think its to difficult, grab a couple of airsoft guns and a buddy, and give it a try. I think youll be surprised at how easy it is to make those shots at reasonably close ranges, even on moving targets while you yourself are moving, and even without sights. (Of course, there is the assumption that you normally practice somewhat realistically here, and hopefully, if and when you really need the skills, its not your first experience at drawing, moving and shooting while you go.)
One other thought here, since you often hear how a 5 shot revolver is all you need to solve most problems. How many rounds do you waste shooting COM with one, until it clicks (and that could very likely be literal) that youre not getting the results you were expecting, and you need to change things up?