Seems like that's all you can ask for if the attacker has physical access to the machine. Would be happy to be corrected though.
It’s one thing if you get physical access, replace the engine control module by a crooked one that will send the proper signals to the ignition and all the other actuators and start the car.
It’s another thing if you talk to the real engine control module (which should already be on alert because the car was broken into) and tell it “trust me, I’m legit, here’s your new firmware” and the computer just runs your code no questions asked.