f2.8 = f2.8 whether the lens is for a tiny P&S or a 8x10 plate camera.
And 35mm is 35mm for any camera. Why is the focal length by itself important? Because you want
equivalent AOV not
equal focal length. Same with f/2.8: you want
equivalent light gathering capability not
equal f-stop.
Sure, the hole in the lens and the total amount of light transmitted by f2.8 for m43 are smaller than f2.8 for FF, but that is not important.
Not important to whom? If all you are counting is f-stop, then the Sony RX-10 is also f/2.8 from 24mm to 200mm. Does it have the same low-light capability? My iPhone is f/2.2 - is that better than the f/2.8 on the other lenses?
What counts is the amount of light per unit area falling on the sensor. And they are equal.
Somehow I doubt you think that's all that counts if the sensor is smaller than MFT - only if larger.