No, the comparison you gave was between walking and cycling - not ebiking.
Exponential is an equation that in this context perhaps suggests the more you use, the worse it gets (unless you are using the word in a hyperbolic manner). Actually, it that's generally not true of bikes or ebikes:
Yeh I did consider doing but thought sod it I'll drop it here...
www.retrobike.co.uk
Ah but that's conveniently ignoring a huge part of the carbon footprint, I'll accept your premise that an electric motor is more efficient in it's use of energy than a human after all the human produces plenty of waste heat as they pedal their bike but once you add in the recharging of the ebike...
www.retrobike.co.uk
The worst bike or ebike is probably the one that never gets ridden. May I suggest you post some stats to back up your gut feel?