I can coast downhill at zero energy costs.
TRUE.
But how far will you travel beyond the downgrade?
And each touch of the brakes you are burning energy, making your rotors warm.
Regen saves it for later.
Converting the original energy to electricity and then charging batteries is inherently going to cost energy. Fossil fuels are plentiful and excellent stores of energy. You drive your electric go cart, I’ll stick with my diesel.