I think the point being missed is that having an exit wound doesn't hurt your odds. Yes, blood leaving the circulatory system is key, and it doesn't matter where it goes, as long as it goes. My point is that having another hole does not reduce the paths available for the blood to take.
It isn't a really quantifiable increase in the odds (I believe it is an increase) but even if it isn't, it doesn't decrease anything by being there.
"Bleeding out" is one method, another is shut down the pump or the major pipes from the pump (bleeding in?) what ever results in the fastest route to 0/0 blood pressure is the most effective.
The "failed" 9mm in the Miami shootout got TO the major pipes above the heart, but didn't any further. It was a fatal wound, but didn't do enough damage to put the shooter down fast enough. Because it didn't penetrate any further. I don't fault the round, there is no magic bullet. That load met all the required specs and had proven itself effective many times before.
As to clothes, and worrying about them, I think its a "they can have an effect" thing, but again not anything quantifiable. I'm not talking about trying to shoot through a Chinese winter coat at 200yds with a .30 carbine, but close range with common pistol calibers.
During the early development period of the modern JHP pistol bullet there were numerous examples of the JHP opening too early and being stopped by clothing, and there were also many times when they didn't open and acted just like FMJ.
Today, everyone says that problem is pretty much solved, and it seems so.
BUT, there are still reported cases where heavy coats seem to affect penetration. Not too many months back a guy in NYC took several 9mm hits that were reported to have been stopped by his Carhartt coat (and some hits the coat did not stop, as well)
Probably a freak thing, if what was reported was accurate, but something to consider if you are choosing a round on the lower end of penetrating power.