What??? Overfuelling doesn't occur in EFI engines? Mate, my Toyota 2SZ car engine started overfuelling few days back and it started giving 5km/litre. I had to diagnose while fuel system delivery including fuel pump, fuel filter, air intake system, injectors, plugs, coils, fuel rails and all the sensors including MAF and O2 sensors. I also had to examine the cooking system since temperature malfunctioning caan seriously affect fuel consumption. In the end the O2 sensor was found to be dead as well as a bad leaking air cleaner assembly. EFI doesn't mean that it will always keep giving optimum fuel consumption. One has to take care and maintain a lot of factors.
As far as theory is concerned and the fact that you don't care what theory is about as far as you're getting electricity... No my friend, it's not about just getting electricity. It's about getting electricity in most cost efficient way, preserving the life of engine and keeping engine's maintenance intervals to the minimum required as opposed to getting electricity at the cost of wearing out the engine. That's where the theory helps out in practical application. Thank you