The extra complexity spreads out the load. All of the things that often fail in an engine are less likely to when the engine only operates for a limited duty c

The extra complexity spreads out the load. All of the things that often fail in an engine are less likely to when the engine only operates for a limited duty cycle, for extended durations, and for a fixed optimal load. You have the more robust motor system smooth over all of the transients. So while there are more single point failures the system might be overall more reliable. If simplicity was the only way to make something reliable we would have rickshaws rather than cars.