It depends a lot on how you drive. If you do a lot of hard braking, the car will have to use a lot of friction braking. If you slow down more gradually, the car can just use regen which is gonna be pretty efficient.
Still, I'm not sure OP's train of thought holds. Mass matters because you need to spend energy to accelerate it and move it uphill. Regenerative breaking does not have 100% efficiency. Therefore, energy losses are proportional to weight. Also, isn't tire drag proportional to weight? That's a energy sink that can't be recovered by breaking.