first, Kosha couldn't kill anyone today, only injure them.
unsuccessful assassination attempts are not displayed.
Thirdly, you're delving too deeply into philosophy. Let's also say that shooting someone with a machine gun isn't feng shui. It's been said, big means big.
But on the other hand, Hostor was probably blocked by Shepard (a butt strike), and then he couldn't kill him. Calhoun could have been protecting Plesen, or it could have been G-man (protection is displayed by him).
I guess I'll agree with the machine gun and Grant version. Otherwise, it just doesn't make sense.

Барон "Vampires"
Отдай свои прошлые сны,
В сомненьях себя обрети,
В бешеном танце душа кружится!
Не думай, что будет потом,
Здесь и сейчас мы живем,
Стань хоть на миг сам собой, слышишь!