If you want that number to be lower, which is totally pointless, make a bunch of phone calls. Then voice calls will be 30, 40, even 50% percent of the total usage, depending on how much you talk. Then the screen will have used up a smaller portion of the battery relative to, in this case, voice calls. It might drop from 79% down to 30 or 40% of the total battery consumed.
79% display usage just means that just about the only thing you did was use the display. Since that was the only significant battery consuming activity you engaged in that gets credit for the most usage.
It certainly doesn't mean that it used a TON of battery or that you should even care. It just means it used the most when compared to other stuff.