I'm really not interested, and I'd rather just concede the point. It appears as though you're right.
The definition isn't as important as whether or not people can agree on it. I've stated the definition is informal, and I've stated why I believe it should be defined a certain way. If you're using the guidelines for "Mass murder", then we should replace murder with someone being shot, all other things being equal. If you think I'm wrong, tell me why.