You talked about the degree of suffering changing based on if that person has been helpful in your life. Both people who died suffered the same fate why is it less consequential if the person killed was a stranger?

The person who helped you has done things to make your life easier in some ways. Even then, one commits negative action towards them it has a higher degree of suffering attached to it. Although both a stranger and this person suffered the same fate, it is your actions and your Karma that is important here.