I believe they use different style motors. Rattan pushes their regen, so that has to be direct drive. Rad, I know, uses a geared motor in its Radmini.
Given motors of similar size, a geared motor will pull better on a hill while the direct drive motor will have a higher top speed. That would imply that from 0-15 mph the Radmini might win in a throttle only race, but it cannot get the top speed of the Rattan. If they have gone to a larger motor in the Rattan, this could change.