See my other posts, I've already covered this. To recap, killing others, "weeding out the weak" doesn't make others stronger, and such a system can cause the weak, cowardly and unwilling to protect to float to the top over the dead bodies of strong and courage protectors. Also weaker inexperienced people can become stronger and experienced, ESPECIALLY MAGES, but not if they are dead. So even if you care nothing for lives at all, such a stupid system is counterproductive.
back in the day people did not arrive unannounced, the very act would have been considered very rude and scandalous, the palace was notified in advanced that the duke would be coming, giving them enough time to prepare for his arrival, as is the point of announcing them ahead of time.