Sensor in the vehicle is way more responsive and reliable than anything remote (EM emission based).
Further Discussion can be found at /r/Formula1 [1]
Alonso (or others in the team) had likely run Pouhon flat in a simulator. He, and his engineers, knew it was within the realm of possibility for the car. But, to what level of detail do McLaren's simulations model the energy system? Do they run real ECU code/parameters? Probably not.
The ECU is a sealed unit made by a single supplier. It has a finite number of sensor inputs and can only use relatively simple algorithms to control the power output. Mechanics can pre-program throttle curves for a particular track, drivers can tweak the throttle mapping mid-lap using their steering wheel controls, but the ECU can't do anything that could be regarded as "intelligent".
The engine map has a finite number of allowed inputs and a bunch of restrictions they must adhere to. For example it must be monotonic so that more throttle pedal input means more torque to the wheels.
The engine map can not do anything based on track position, but the drivers regularly change engine maps while on track, especially in qualifying.