I think you've made a very good point. It is not intended to supplant existing jurisdiction, and I think you're quite correct. What is reasonable under the circumstances will continue to be argued, and past cases would be a good indication of just what is reasonable or not reasonable under the circumstances.
You point out something else as well. We deliberately put the list to be non-exhaustive because, as you say, you want the law to develop. There may be other criteria or situations here that we're not aware of or that may develop in the future. We don't want to close it off and say you didn't come within section 2 through 8, so therefore you're out of luck in trying to use this self-defence provision.
The list is a non-exhaustive list, but again this is not intended to supplant existing jurisdiction. You're quite correct. We don't want to be clogging up the courts and taking the time to go over areas that have already been decided, that have already been adjudicated. Much of what we are doing in this law is just clarifying so that it's not overly complicated for any individual or person or agency or court to figure out just what we're talking about when we're talking about the defence of a person or a property.