I doubt there is any one-size-fits-all situation. 10 seconds isn't a lot of time to react.

A lot of variables can impact the effectiveness of bear spray. A breeze, the experience of the user, the size of the cannister, and the sensitivity of the animal to its effects.

A lot of variables can impact the effectiveness of firearms too, especially in a stress situation. As I understand it, it takes a pretty good, fast, disciplined shooter to kill a charging bear. Otherwise, if a bear is doing a "false charge" (for example) it becomes a wounded bear that is "all-in."

If two of the three hunters had used bear spray, with one as a safety, would the outcome have been different? Maybe, maybe not. It's really impossible to say.

I wouldn't wish to see any human hurt. Still, it's a damn shame about the bear.