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.
a strong reason to use a pilot is to protect a large capital investment. in war, you get shot at. things are over stressed, equipment fails.
a pilot has the ability to improvise, and perhaps bring the aircraft back to be repaired and returned to service.
will an AI be as good at 'improvising'?