There is no "the answer" there are an infinite number of potential answers and partial answers and answers when combined with other answers might be an effective answer.
In some cases with some people, just like kicking on attacker in the nuts might end an attack and another it might piss him off enough to kill you anyway, One shooter, a laser pointer in the eyes may not mean much and another, it blind him hard enough to scare him enough to break off an attack. Being a welder I have known people that need very little filtering to see and others that need the darkest lense or will suffer.
We, You and I and everyone else can not possibly know how any defense will work on any specific attacker or shooter till we try.
The point in all of it is to "do something" don't just stand there saying nothing will work while innocent people are being murdered.