Wouldn't you be able to pedal at your most efficient rate, and go at whatever speed you want? Like how diesel-electric trains don't actually drive the wheels with the diesel engine, they power an electric motor.
(I've never ridden any kind of e-bike so I don't really know how it works)
Bikes have very efficient transmission systems, so outside of extremes you can pedal at an efficient amount of torque for the rider regardless of say: hitting a big hill. This is doubly so for e-bikes that assist in the pedaling.
This is more akin to a hybrid car, who's gas engine could generate electricity, but in the case of this e-Bike from Rivian, why would you do that? The electric motor is significantly more powerful than a person's legs, outside of the Pro Peleton.
Watch anyone on a Class 3 ebike: they're not pedaling. The bicycle drivetrain is just there to get around regulations, like having a license.
Rivian isn't known for making hyper-efficient electric vehicles. Rivians are MANLY trucks made to do MANLY truck things, like go fast! and go through tires faster!
Trains and large trucks use this setup because a mechanical gearbox would need to be enormous to withstand torques they produce. Bikes don't experience even moderate torques so they can be equipped with 10-20 geared transmissions, which weight under 1 kg.
On my e-bike, with just a standard 7-speed transmission I can pedal at my most efficient rate always; since I have an extra 300W of power available I don't need the super-low gears for climbing.
No one is going to do that. It's an electric motorcycle in disguise. Don't even play.