I think you're wrong about carbs. They are the best technology for low-cost, low power aero engines. There is nothing inherently inefficient about them. Aero engines can and do run lean, which is where you gain your efficiency, so there is no need to have precise lambda-1 control that automotive engines require (only for three-way catalytic emissions control mind!)
Fuel injection systems require high pressure fuel pumps and, if electronically controlled, usually wind up having some kind of electrical dependence which requires redundancy. More weight and lots of complication. Then, once you've introduced software and electronic control, you have a bunch of serious QA issues you have to deal with.
I agree that FI can be made to run efficiently more of the time, but a carb can be just as efficient enough of the time. When you're burning 15L/h it doesn't make any sense to burden yourself with 15kg extra weight and complexity just to make it 14.5L/h.
Horses for courses.
A