^Actually shooting Peter in the head probably would have killed him. He copied regeneration not god mode.
In ep 20, it seem to me like everyone knew how to use their power(s) very well, very close to mastery. Even Peter, who was the worst at controlling his powers, utilized most of the abilities we've seen him copy. I don't mind seeing the heroes actually train to further develop their powers since it's much more realistic. If the current Peter and Hiro got too powerful without a worthy antagonist, the story could just become inconsistent.
etufo: HS is most likely going to die sooner or later. Who will kill the cool character killer?
Popo: well, obviously going by that logic, HS will have to kill himself...