As a matter of law, "ownership" and "control" are two distinct concepts. Similarly, "power" and "right" are two distinct concepts.
If I have car keys, I have control over the car associated with that key. That is to say, I have the power to drive it around. Whether I have ownership over the car depends upon a panoply of factual circumstances that are as varied as every day life.
Similarly, if I possess a private key, I have control over the coins associated with that key. That is to say, I have the power to dispose of them. Whether I have ownership over them depends upon a panoply of factual circumstances that are as varied as every day life.
A well thought out statement. In our current world legal ownership is authorized by government but how would that be possible with bitcoin? The moment bitcoin ownership comes by a third party authorization it stops being bitcoin. And even if such a third party authorization comes about without any protocol changes it would be about as practical as tilting at windmills.