You may be over estimating how much power a modern laptop backlight consumes and may be under estimating how much power a modern CPU/GPU consumes at idle. They are both significant factors.

On your computer reading this, you're probably not moving the screen. That is time that the GPU can sleep. That is a lot of power saved, regardless of display.

So yes, "generating all this light" takes up a lot of power. But just because it does, doesn't mean that overall battery life wouldn't be benefited from improvements elsewhere.

And in fact, the average backlight is about 5w, maybe 10w. The average laptop GPU when idle and awake, consumes about 5w as well. If you can get that idle GPU consumption down substantially, that's a potential 20% (or more!) improvement in battery life.