Right, lower weight is better; all else being equal. And yes, higher weight adds to rolling resistance. Of course, coasting energy = acceleration - aero and rolling losses - necessary braking. I was a guest member of the Edison2 X-Prize team remember, and I paid close attention!
And regenerative braking is only available on EV's and hybrids, and is lossy.
But aerodynamic losses completely swamp all other friction losses, often by orders of magnitude; at all but school or local residential zone speeds. Aerodynamic losses are total.
The two vehicles that are case in point for the aero drag being more important than weight are
Allert Jacobs Honda streamliner, and
Dave Cloud's Dolphin. Also, the
X-Prize Knockout Round results confirm this.
The most important factor for high efficiency is the drivetrain.
The second most important factor is aerodynamic drag.
The third most important factor is weight.
Rolling efficiency is critical and must be good, but is the easiest to achieve.
Obviously, all four of the critical factors are interrelated. ICE drivetrains may be lighter than EV's, but they require more cooling, which adds aero drag. EV drivetrains are 3-4X more efficient, and make regenerative braking possible, but they tend to weight more. Packaging an EV is a bit easier, because the motor(s) are more compact, and they have no exhaust system, and they have minimal cooling requirements.