Not true at all.
Hey, I'm all for physical fitness, but in no way is "Physical endurance is crucial in surviving real world gun shoots" the truth.
There have been way too many documented cases of (to put it kindly) out-of-shape folks who have prevailed in real world shoot-outs.
And it wasn't because they outran their adversary, or out climbed their adversary, or had better cardio-vascular conditioning....
It was simply because they were able to shoot their adversary before being shot themselves.
When it comes to shoot-outs, superior physical conditioning is not as big of a survival factor as some seem to think.
Remember, before guns were invented the strong preyed upon the weak.
But due to the invention of guns, even a weak and frail 90 year old grandmother, with emphysema and toting an oxygen tank around, is capable of taking down an Olympic level athlete with one shot.