It’s simple physics, really. A lighter vehicle requires less fuel (in this case, electricity) to accelerate. This means that electric cars are almost always able to be more energy-efficient than gas-powered vehicles as well as more powerful, as less energy is being wasted in propelling a heavier vehicle.
The plastics used in electric cars aren’t the same that you’ll find in a Happy Meal toy, though. Carmakers use advanced polymer plastics, which are impact-resistant, durable, and made to withstand a whole range of driving conditions, including extreme heat and cold that can quickly degrade other types of plastic.