I don't know why everybody focuses so much on the top of the wing. Relative to ambient air, the pressure above the wing is slightly reduced, but the pressure below the wing is massively increased. That massive increase is far more important than the slight reduction above.

We know this, because simple, flat airfoils are capable of flight. Think: paper airplanes, simple balsa models, etc.

The shape of the airfoil is not actually very important for lift. You can make a brick produce plenty enough lift to maintain its altitude, if you can provide sufficient thrust and control it's attitude.

The specific shape of the airfoil is primarily important for minimizing drag across a variety of speeds and angles of attack at various loadings. This is where the top surface of the wing becomes important. By maintaining the flow over the wing, drag is reduced, and controllability is maintained.