When your stare causes Hellfire to erupted then yea. It was a strike to the Heart. But What else is in the Chest? Both Lungs, Liver, Pancreas, Intestines, Esophagus... just about everywhere inside the Chest/Abdomen area lies a vital organ which once injured will lead to your death sooner or later.
My point is, the Gentle Fist directly attacks your internal organs, and kill-zones are all over the body, so if I set out to really go on a murderous rampage then the slightest of touches is extremely dangerous. Neji gave Hinata Heart damage, and he wasn't even trying to kill her.
I've simply never gone for murderous blows against other characters (except Kidomaru cause Shen was asking for it)
Just saying, this view of the Hyuga takes them to overpowered territory and the only reason anyone in our cast can survive against them is the whims of the user holding back. And I don't like that personally.