If they did for some chance keep walking after getting hit, a follow up shot should surely slow them down no matter the caliber. If stopping the person from coming at you is the goal, then I think in most casses, the caliber probably does not matter. There will always be an exception to the rule but For the most part that is how I see it.
Apparently, after ZILLIONS of threads and discussions on the subject, as well as accurate technical data involving real shootings, you have, without reading any of them, created your own theory and expressed such wisdom as "a follow up shot should surely slow them down no matter what the caliber."
A couple of points:
1. A person with a gun doesn't have to come at you. This may come as a shock, but he can actually kill you from a distance.
2. A substantial number of people who have been shot, don't know it at the time. A fatally shot person may still kill you, since adrenaline is a powerful drug in it's own right and both good guys and bad have continued to fight after receiving serious, or even fatal, wounds.
3. Using normal thinking to judge the actions, or reaction to being shot, of a doped up criminal whose thinking is anything but normal, might be a mistake.
Something else to think about, is that the criminal mind set would more likely be to "come at you" before you knew what was happening, and long before you had a chance to draw your gun.