I’m disagreeing with your statement that “you’re only allowed to use deadly force in proportional response,” not with whether this case is being prosecuted rightly or not.
Mate, read that link I put in there. I can tell you, from experience, that if you shoot at someone stealing your property in Texas, where that penal code I posted is from, that exact portion of the statute is going to be used and you will not be convicted. It really is “anyone could have a gun or knife.” At least Texas has it so just theft has to be during the nighttime, so I guess that’s something.
You’ll also get similar worded statutes in many other states in the US, several of which, stating this again, where I’ve had the misfortune of having to research those laws. And that “reasonable belief” part about exposing yourself to risk of serious bodily injury or death? I have seen it applied to people who are simply physically larger than you. Proportional response is a moot concept.