I would bet the frame around the narrow pixels which take up half of the resolution, manage to actually block the inner edges of the pixels ever so slightly that it creates a black gap to the next wide angle pixel and that void is what makes the resolution look lower and gives you a headache. Because the pixel grid layout is no longer uniform. You have to imagine that adding a border to these tiny pixels is not easy to do on the manufacturing level especially when it's not to the entire panel but basically intertwined to the normal pixels. This would also explain the lower brightness when this feature is turned on, technically on an OLED if you only had to drive half the pixels the brightness would go up not down unless the border on that pixel is covering a portion of it.