My 2016 Electra EFI (still with fuel injection) is the best starting bike I've owned. From hot, cold, or been stood for weeks, it’ll start apparently instantaneously. The only non-standard item is a Harley Davidson silencer, which was to reduce weight. My other bikes are a mix of carburetter and fuel injection and they don’t start as quickly. As for the kick start, that’s been removed. Why knacker your joints when there’s an electric start.
On the air bubble theory, I can’t see how that can arise. The injector body and fuel line have fuel at about 45 psi. If the injector was not fully closed when de-energised, the mixture would be too rich. Also, when the engine is shut down, that pressure might be relieved back through the fuel pump into the tank, but there’s still a head of fuel in the tank that will maintain the fuel pressure above atmospheric pressure. So again, no air can enter the injector body or fuel line.