I tend to fire at centre of mass in Arena because I know no one is ever going to stand around and take it anyway, though from that article it sounds like someone could convincingly just stand there and take the shot with little to no consequences in the short term. I still refute your initial claim that it's the best place to be shot, but I suppose it isn't as bad as I assumed, if the article is to be believed at any rate. I was more convinced by a medical document I read saying gut shots had about an 88% survival chance. 

I should also point out I rarely if ever shoot to kill in Arena, 
1. because it would be a shitty way to end a fight
2. Few people would ever take the hit