Even if it was true that software engineers that don't work for FAANGs can't develop something complex (I doubt that's true, I'm sure there's plenty of skilled software engineers working at Lockheed Martin), FAANGs don't employ a lot of aerodynamicists, flight dynamicists, weapons engineers, material scientists, experts in radar technology etc. though, which is just a selection of the kind of specialists you need to develop a fighter jet.