I dont understand how an "acted" fall can help you learn. If the purpose is to fell an opponent, how will you learn if he falls by himself? Aikido is a martial art, not a dance or partnership.
You're right, if uke is falling entirely by himself, nage can't learn. That is why uke must apply a sincere effort. How much effort uke applies is based on the ability of both. Someone with no experience throwing whatsoever will usually have a hard time learning how to throw me if I don't adjust the power of my attack...in other words, I let
them throw me, but they are still doing the throwing.
And many people would disagree that Aikido doesn't involve a partnership.
at its broadest level means to connect with the energy around us purposefully. Whether it's a fist coming at your face or a partner stepping toward you in swing dancing, the question is the same: how shall i move with it so I can maintain my rhythm unbroken?