Death... would have been something else if the father asked MC to do it instead of just watching. Because here he just realize that he's simply not reading to lead war and face the death of his soldiers and of the enemy. To be eeady to kill if he comes to be in a pinch or to deal the final biow to someone already at death's door is something else and completely different.
We could take into account that his subordinates (the butler and magician) are different, it's because they're prepared from the bottom of their hearts to kill in order to protect him. True, he's only and still a kid now, but some even kill earlier than his age... (be it in reality (and maybe the past for whatever reasons/circumstances) or in fiction...).