Regarding the complexity, I believe Toyota has been ahead of the (hybrid) competition for many years, but a PHEV still has two different systems. Everything that can go bad on a pure EV (battery, electric motors, charging system) is there and even if the ICE part is simpler, it's still something that can break.

With this said, other reports of batteries going bad on old Prius, I haven't read much about them being unreliable, so it should be fine while the car is fairly new.