You would be amazed at what you can get out of the stock EFI system with some "tweaking". It is tunable, just not very easily. Tricks include adjusting the AFM spring tension and potentiometer needle location. I've also added a variable resistor pot to the temp sensor to richen the mixture under all conditions. Higher fuel pressures and different injectors can also be used.
The problem is it is trial and error for the most part. Stop, make an adjustment, drive, repeat. Using a wide band O2 helps. And of course, you will never get it as close as a fully programmable system.