I think you need to put forth your definition of high fantasy, because it doesn't seem like you're using one I'm familiar with. High fantasy isn't about extremely powerful people, but about plots that have large stakes and scale. Lord of the Rings is a high fantasy work because it's about an epic confrontation between Good and Evil that determines the fate of the world. To make D&D do high fantasy, you just have to run plots that are of appropriately great scope.