The extra weight of a battery and electric drive train means at least part of the fuel efficiency is compensated, hybrids typically weigh 200 Kg more than their ICE counterparts.

There's another measure that would have saved everyone a lot of money and emissions: better aerodynamics. Car makers have been building terrible designs for decades because gasoline was cheap, but we know they could do much better. A car with good aerodynamics (like the Prius by the way, or the Hyundai Ioniq) saves enough fuel to not need a hybrid drive train.