I doubt seriously if the aileron on the CAP 232 weighs 70 lbs. However it isn’t just the weight but also the moment arm that must be taken into consideration. The aileron is fairly narrow so that the cg is relatively close to the hinge line. The balance weight is extended pretty far forward on a sort of pylon beneath the surface. (There is also the possibility that there is additional weight in the aileron leading edge, which would not be obvious from the pictures.) The little triangular surface on the forward edge of the pylon is what gives the aerodynamic force to lighten the control force. I suspect that the size and shape of the surface was experimentally determined.

The size shape and location of any aerodynamic balance affects the slope and shape of the stick force gradient. For aerobatic aircraft the stick force gradient is tailored so that the pilot can fly the required maneuvers without being tired out by high forces, but the gradient must still be enough so that he has a good feel for the airplane.

I think what is confusing is that there are two independent factors. First the surface must be mass balanced such that the natural frequency of the surface is not in the range of forcing frequency at the speeds at which the aircraft is designed to operate. This doesn’t necessarily mean on the hinge line. Many small aircraft that operate at lower speeds have surfaces without additional mass balance and the cg is well aft of the hinge line. Flutter only occurs when the natural (resonant) frequency of the surface and the forcing frequency at a particular speed coincide.

On the other hand, aerodynamic balance is for the purpose of changing the stick force gradient, usually to lighten control forces. This frequently involves putting some area ahead of the hinge line that will protrude into the air stream and add a force to assist moving the surface.

In the case of the CAP series aircraft the designer has chosen to use the same hardware to accomplish both purposes.