How are those more accurate? Colloquially, to be "on autopilot" describes how one can mindlessly perform familiar actions which don't require novel thought. For example, walking home from the train station. I'm sure plenty of people have been injured or killed while walking around "on autopilot."

In the context of a software feature, "autopilot" implies a computer control system which is capable of maintaining rudimentary ongoing control of the vehicle.

Whereas a co-pilot is a whole other pilot. Surely that's worse, implying equivalence to a human sitting next to you, with comparable levels of training and skill, intuitively capable of taking over at any time. I wonder what would happen if Ford developed a system and called it "Co-pilot". We might never know.