My bad, I was thinking that the tire drag doesn't decrease, but you are correct that although the rolling resistance coefficient doesn't change, total rolling resistance does in fact decrease by 10%, but all other losses remain unchanged. Aerodynamic drag is the biggest thing sucking range though (at speeds where we care about range) and other losses (conversion losses, resistive heating losses, and use by non-drivetrain components) do not change.
With heavier car you need more energy during acceleration. More energy means bigger current which means bigger conversion losses and resistive heating losses.