In most of those throws you are not supposed to be carrying to full weight of uke. It only looks like you are, but actually you are not (should not be) because one side of uke is going down as you lift the other side. You are just the pivot point. Obviously you can add more power to it and lift uke completely, but it is not a strict requirement. Even ura nage, if performed with the right placement in sacrifice motion, much of your power is in the horizontal direction and the lifting part lifts uke's bottom half like a lever.