Rear wheel bearing stiff (high friction)?

When you are spinning the rear wheels do you hear the brake shoes rubbing against the drum? If yes, then you could adjust the brake shoes by turning the star wheel accessible via a slot in the back of the drum.

If you don't hear the brake shoes rubbing, then the level of friction is what it is. The hub bearing has to support 800+ lb and withstand 100+ mph speeds so it is going to be more substantial than a bicycle bearing that supports ~150 lb and only has to travel at ~30 mph.

The RPM of the bicycle wheel is even lower than the relative speeds would indicate since the bicycle tire has a much greater circumference than the auto tire.

 

So you have the rear road wheel and brake drum off. And you attempt to spin the wheel mounting plate? It will never spin like a bicycle wheel. Automotive wheel bearings are far larger, have far more friction and are far more durable than a bicycle's. If you consider what is expected of both assemblies, it becomes clear why. A bicycle's wheel bearings are cute little dainty things and need to offer up VERY little friction to be effective. On a gas car, there is plenty of energy to waste, and orders of magnitude more force acting on those bearings. So they're bigger, stronger and will always offer more friction. It is normal for that mounting plate to not keep spinning without constant power input. All cars. Not just the Prius.