In the abstract that might be true, but you're missing issues of unnecessary complexity which feed into systemic risk. Large airplanes are obviously different

In the abstract that might be true, but you're missing issues of unnecessary complexity which feed into systemic risk. Large airplanes are obviously different to cars and so are the engineering choices. It actually makes a lot of sense to use fly by wire in an plane because the level of existing complexity (and expense) justifies it. A Boeing with triply redundant mechanical control of control surfaces is still inferior to Airbus fly by wire when the latter can implement a more reliable system, but only because the inherent complexity and expense of planes allows it. The Airbus will have 5 or 7 redundant electrical paths to the control surfaces and numerous redundant power supplies and actuators and beats the mechanical system hands down. On a car you sharply increase complexity, and therefor reduce reliability. You need redundant power supplies and power connections, for instance. Planes have to be serviced by certified professionals on a strict basis, where as cars do not. So you have to implement a system that still operates under conditions of neglect, all while having severe cost limitations.