Kill joy defense maters a lot.
In the K/d it maters.
In the Point catagory it maters.
In the kill per sortie it maters.
And killjoy I have flown a game where at one time living was the primary goal of the score system, just as you sugest. What you are not seeing is that not just you would adjust your tactics, everyone does, and hence most of the people will not engage unless they have an advantage. This leads to everyone running, because if you do not have the adanatage you would run untill you did, then the other person runs untill he has the advantage.
As to energizing the comunity, what you sugest realy would be the death of the comunity.
Our score system is the way it is, because we have tried many different ones in the past.
HiTech