This is what you would describe as "Aiki"? I would describe what you are talking about as "proper technique" using Mechanical advantage. Would you agree or disagree?
I think it is much more complex than this. If this is the case, then there is no difference between Judo and Aikido.
D) A body skill, that once acquired, allows your body to automatically adapt to movements and changes made by an attacker/opponent, that make the opponent feel strange, weak, unable to adapt to you.
I think this is because there are certain positions where if you put that body in those positions he is unable to adapt or regain his balanced state. An example is the upturned palm during the ikkyo pin. An ikkyo pin can actually be done using just a thumb on the elbow as long as the palm is facing upwards. With minimal contact, uke won't be able to move. But if the case is that uke's palm is turned down during the pin, he can easily regain his balanced state no matter what weight you put into the arm.
This is not mechanical advantage in the sense that the resistance, fulcrum and lever are in the same locations for both cases, the only difference is uke's palm if it is up or down during the pin.
This palm up case is also applicable when you are doing kuzushi in preparation kotegaeshi and other techniques meaning that that side of the arm is weakest if facing up. Uke can't do anything during kuzushi. There is also the feeling from uke that he is being drawn to nage. Your role as nage is to find these positions and manipulate uke to assume those positions.
so I think it's
D) A body skill, that once acquired, allows your body to automatically adapt to movements and changes made by an attacker/opponent, that make the opponent unable to regain his balanced state