[dcb]

Basically you have to oversize your motors/battery/controller if you don't have a transmission, which could conceivably cancel out the space savings of hub motors (and cost).

And oversized is not optimized. It is going to be heavier than it could be with a couple gears. Electric motors also have peak efficiency under the right conditions, you can approximate those conditions more closely/frequently with gears. Gears do not have to be horribly inefficient.

Also this mass is not just unsprung, but it is spinning. You spend more energy accelerating and decelerating (and trying to change direction).