Fighter jets don't need 100%. In a war, we accept a much higher rate of casualties than we do in day to day driving. I would also imagine that while planes are harder for a person to pilot, they are easier for a computer. Most of what makes them hard is mechanical, not dealing with unexpected situations.

I reject the notion that planes are harder to automate.

There are many ways that flying is an easier solve than driving, believe it or not.

Planes might be easier, large empty space in the sky