Your picture of how lift works is fairly off base.
The speed difference being due to asymmetry is wrong. Symmetric wings still generate lift by having air flow over the top faster than the bottom. Symmetric wings flying upside down also still generate lift that way. Asymmetry helps, but is not necessary.
The important thing to understand about aerodynamic lift, and that few people do understand, is that the Bernoulli's principle action and the air deflection action are the same thing. They are not two different mechanisms which act in concert. They are two different ways of looking at a single phenomenon.
If you deflect air downwards, you will generate a speed and pressure differential between the top and bottom of your wing. The pressure differential will produce an upward force on the wing that is precisely equal to the downward force on the air. Likewise, if you generate a pressure differential between the top and bottom of the wing, you will deflect air downwards. They're two different results of the same action.
To truly understand why wings generate lift (which is the same thing as why wings generate a faster airflow over the top than the bottom, or why wings generate a lower pressure on top than on the bottom, or why wings deflect air downwards), you need to understand the Kutta condition.
A wing moving through air has two stagnation points, which where the airflow splits. There's a stagnation point at the front of the wing. Any air above that point goes over the top, and any air below that point goes underneath. At the back of the wing, the stagnation point is the point where the air from the top and bottom meet again.
The location of the front stagnation point depends on the angle of attack. If the wing is flat, the front stagnation point will be right at the leading edge. As you tilt the wing upwards, the front stagnation point moves toward the underside of the wing.
The Kutta condition says, in short, that air won't go around a sharp corner. Thus, the rear stagnation point is always at the trailing edge of the wing. This is why wings are shaped like a teardrop, and that sharp edge at the back keeps the rear stagnation point from moving around.
With the front stagnation point mobile, and the rear stagnation point fixed, you have an asymmetry that causes circulation. This is a rotational component to the airflow around the wing which causes air to flow over the top faster than the bottom, such that the stagnation point is at the trailing edge. This circulation causes the air to be deflected downward, and causes lift.
In summary, wings generate lift by deflecting air downwards, which is equivalent to saying they generate a pressure difference between top and bottom, which is equivalent to saying they generate a speed difference between top and bottom. Wings accomplish this by having a sharp trailing edge, which causes circulation that deflects the air. Wings are shaped the way they are not because the asymmetry is necessary to generate lift, but merely because it's more efficient that way, by changing where the front stagnation point occurs, or by generating less turbulence in the air.
The speed difference being due to asymmetry is wrong. Symmetric wings still generate lift by having air flow over the top faster than the bottom. Symmetric wings flying upside down also still generate lift that way. Asymmetry helps, but is not necessary.
The important thing to understand about aerodynamic lift, and that few people do understand, is that the Bernoulli's principle action and the air deflection action are the same thing. They are not two different mechanisms which act in concert. They are two different ways of looking at a single phenomenon.
If you deflect air downwards, you will generate a speed and pressure differential between the top and bottom of your wing. The pressure differential will produce an upward force on the wing that is precisely equal to the downward force on the air. Likewise, if you generate a pressure differential between the top and bottom of the wing, you will deflect air downwards. They're two different results of the same action.
To truly understand why wings generate lift (which is the same thing as why wings generate a faster airflow over the top than the bottom, or why wings generate a lower pressure on top than on the bottom, or why wings deflect air downwards), you need to understand the Kutta condition.
A wing moving through air has two stagnation points, which where the airflow splits. There's a stagnation point at the front of the wing. Any air above that point goes over the top, and any air below that point goes underneath. At the back of the wing, the stagnation point is the point where the air from the top and bottom meet again.
The location of the front stagnation point depends on the angle of attack. If the wing is flat, the front stagnation point will be right at the leading edge. As you tilt the wing upwards, the front stagnation point moves toward the underside of the wing.
The Kutta condition says, in short, that air won't go around a sharp corner. Thus, the rear stagnation point is always at the trailing edge of the wing. This is why wings are shaped like a teardrop, and that sharp edge at the back keeps the rear stagnation point from moving around.
With the front stagnation point mobile, and the rear stagnation point fixed, you have an asymmetry that causes circulation. This is a rotational component to the airflow around the wing which causes air to flow over the top faster than the bottom, such that the stagnation point is at the trailing edge. This circulation causes the air to be deflected downward, and causes lift.
In summary, wings generate lift by deflecting air downwards, which is equivalent to saying they generate a pressure difference between top and bottom, which is equivalent to saying they generate a speed difference between top and bottom. Wings accomplish this by having a sharp trailing edge, which causes circulation that deflects the air. Wings are shaped the way they are not because the asymmetry is necessary to generate lift, but merely because it's more efficient that way, by changing where the front stagnation point occurs, or by generating less turbulence in the air.