Remember that 30% of the light is reflected off the pellicle mirror to the AF module. Only 70% will pass through the mirror and reach the sensor. This is the same problem that my EOS RT faces. 30% approx equal to one third stop loss in light reaching the sensor.
Err... That means a lens in F2.8 is now F4 or just the amount of light being used by the sensor is 70% of the total light captured by the lens?