Follow the legal reasoning. Per the law, to use a firearm against another person, even just to threaten, is to use deadly force. Even if you don't actually fire, you have still used deadly force.

The use of deadly force in self-defense is only legally justified if the threat you are defending against is also a deadly force threat, armed or not. So, if you state you felt a deliberate shot to the leg (which can easily kill or maim regardless) was "sufficient" to stop a threat, almost by definition you did not feel that threat was actually serious enough to justify using the gun at all. If you didn't think the attack constituted a threat of death or grievous bodily harm, why were you shooting?

Firearms cannot, by law, be used as "less lethal" defensive weapons to ensure compliance or to counter non-lethal threats, regardless of your intent. If they aren't threatening your life, you don't even threaten with a gun, much less shoot. If they are, you shoot to stop, not to wound.