Hello Jakus,
This is an interesting topic, and not being a Sheldon Cooper, I was working from what I call common sense physics. Let me explain my thought process.
I agree the published performance of the fans reflects free flowing conditions, and are not accurate for real world application. But relativity remains... what I mean is, if fan 1's airflow specification has double the capacity of fan 2's airflow specification, in real world situations fan 1 would still have the greater output.
You state:
The airflow generated by the rad fans just supercharges the flow through the large fans and vice versa. The large fan is moving air into a negative pressure environment which automatically means they generate more flow than they would in a static air free flow environment.
It's the "vice versa" part I question.
As you say, the Rad fans would create a negative pressure inside the radiator, which creates a greater pressure delta across the fan at the top,
in the direction of flow, and will consequently increase the airflow through it. But conversely, the negative pressure inside the radiator will cause a greater pressure delta across the rad fans,
against the direction of flow, and would have a detrimental effect on output.
Push-Pull works because the push fan increases (supercharges) the inlet to the pull fan. If the push fan were not able to at least meet the inlet requirement of the pull fan, i.e. be restrictive, the setup would not work. The same is true for dual pumps, If the output of the first pump did not exceed the input/supply need of the second pump, there would be a loss to the output of the setup.
The negative impact may not be too noticeable in the proposed gigant setup because the bottom is still open and will make up the difference. But I believe the top fan will not be a positive contributor to the overall scheme.