In 6th Edition, we use Professional Ratings for the NPCs (SR6, p. 203). When the NPCs boxes of damage exceeds their Rating, they make a Composure Test (SR6, p. 67) to see if they stay in the fight or run away, that way you don't have to adjust their health. I can't speak on making the action scenes more compelling since I don't play 5th and haven't looked it's Combat rules in a decade.