Leonardo da Vinci, notable designer, and many other sophisticated people considered flapping wing aircraft. It’s easy to dismiss it as simplistic hundreds of years later once practical solutions already exist.
No, flapping wing aircraft simply are less efficent for size scales that can carry a person. That's why the larger a bird's wingspan, the less frequently they flap, such that condors, storks etc. are basically fixed wing gliders.
We in the artificial world do have our own local optima with quad copter drones. Flapping here would be more efficient. Consider seagulls that dive and change direction instantly, and can respond to gusts without missing a beat. We have nothing approaching that maneuverability. This is an active area of research.
What do you mean 'no'? It's an empirical fact that very talented designers considered flapping wing flying machines, before they had the information that we have now. They were not 'overly simplistic' except in deep hindsight.
We aren't done designing flying machines. Maybe it will turn out that when we have sophisticated enough control mechanisms and materials, flapping will turn out to be the way to go after all.
Of course natural evolution has found only local minima in the fitness landscape, but as a designer it's been running its algorithm a lot longer than humans have. Its local minima may well be better than ours, and so worth trying to imitate.
