"owns a gun" is a weird way to say waving it in the air after the police have told him to not have it repeatedly.

You can say "de-escalating the situation in a way that preserved this man's valuable life" now that you have the hindsight that he wasn't a threat.

The reality is though, police officers turned up at this house with no real information other than the fact that there's a drunk and drugged unknown criminal saying that he's tired of the police following him and that he has a "gun with no bullets in it". They told him 4 times on call to not have the gun on him when they arrive.

They turn up, he's outside with a gun in his hand, holds it in the air even after being screamed at, and the officers have to react in seconds to this person who could easily pull the trigger and kill someone.

There's no way that the police can know he isn't going to kill somebody right then and there, "de-escalating the situation in a way that preserved this man's valuable life" is not a certainty, it's a risk to other people's lives too.

And like I said, "Whether guns are the best way to neutralise someone in that kind of situation is a debate to be had.". I live in the UK, neither the police nor citizens have guns so tasers can be used instead. America has an extra layer of risk in these situations.