High ground does give advantage in real life combat; and there are plenty of reports of people exerting themselves amazingly for short periods (historical berserkers come to mind).
If you think it's easier to hit a target 100m away from you with a bow when you're higher in comparison than if both of you are on the same level... You never try archery...
In arena such in BG3, you wouldn't have any advantages in real life because most of the time, there isn't any obstacles
