As others have mentioned, it's a matter of jury perception.
- Yes, if it's a "good shoot" it won't matter. But you're not the one deciding if it's your intentional act of extreme violence against another person was justified. If the DA/grand jury does not agree with you that it was justified, it won't be a good shoot unless your trial jury decides it was.
- Jurors can be influenced by all sorts of thing. We know from post verdict juror interviews that Harold Fish's jurors were troubled by his use of JHP ammunition. And our own Glenn Meyer has written this excellent paper on the effect choice of self defense weapon can have on a jury.
"It is long been a principle of ours that one is no more armed because he has possession of a firearm than he is a musician because he owns a piano. There is no point in having a gun if you are not capable of using it skillfully." -- Jeff Cooper