The 21' rule only applies if you are unaware of your threat and do not have your gun drawn. If you're pointing your gun right at them, it's much, much less than that. That's why people don't try to attack someone who has a gun on them at 10' away.
Regarding the "statistic" for "murders via guns", we've already shown it's a useless measure. If "murders via guns" goes down but "murders" goes up, along with other violent crimes, is that a useful change? No, because the tool doesn't matter, only the result.
Another "statistic" that is meaningless is that if you have a gun in your home, you're much more likely to die with it than to use it in a home defense. This is only true because when people want to commit suicide, they use a gun if they have it.