Reducing weight sure is the most effective way to improve efficiency.
The best Tesla model 3 uses 25 kWh / 100 miles and weighs two tons. A top of the line cargo bike like the Tern GSD is capable of carrying passengers and luggage using only ~1 kWh / 100 miles, because it weighs only 75 pounds.
Slightly reducing the weight of the battery pack in a full sized car is missing the forest for the trees when it comes to lowering transportation emissions. As long as we're supply constrained for lithium battery cells, those 50 kWh of batteries going into the Tesla would be better going into 50-100 e-cargo bikes that each take a car off the road.