@Kynnath
As twinklecake said, it's more about breaking his mindset, ars never thought he'd have to go to war or deal with violence, now he's faced with the facts of life of a lord, not only must he be prepared to kill, he must also be willing to put on a strong face for his soldiers, because a army's strength is in both the faith of their commander, and his ability to lead and if need be, fight and die for them, many armies throughout history fell not due to enemy numbers (in fact, there are well known battles of a small group of soldiers beating back or at least fighting a vastly superior force and either winning or making the victory too costly or pyrric, the most famous western one would be the battle of thermopalae and the 300 spartans and of course, alexander the great's vastly inferior numbers but vastly superior leadership, the japanese probably look more at the battle of okehazama and the failure of leadership of yoshimoto imagawa vs the vastly inferior nobunaga forces though) but due to their leader's incompetence, if ars had led his father's forces in battle it's likely they would have lost and ars realized that, his training is basically to prepare him to kill, it's never easy the first time to do so, but he must be prepared to do so.
@mahtan
While i'm not gonna spoil anything from what i've read of the novel, if i was to guess ars is probably a average to above average warrior but a amazing leader and commander, mainly due to realizing his faults and trying to improve them, this of course can change after all but so far that's what it's looking like to me.