Here is a test for stiffness. Turn the radio on. Grab the trailing edge of the aileron and try to deflect it. Do it several times grabbing it at different spots along the trailing edge. Apply at least two and preferably three of four pounds of force to deflect the aileron and see what gives. Some servos are low torque around neutral. If the servo gives then replace them with digital servos of sufficient power. If the linkage gives, replace it with a stiffer linkage. If the aileron bends, then stiffen it top and bottom, with a skin of 1/64 ply under the covering. If the hinges give, then replace then with heavier pinned hinges.

Make a counter ballance weignt or two or three. Insert the wire of the counter balance in the leading edge of the aileron so that the weight extends into the inside of the wing ahead of the aileron. Make the weights heavy enough that the aileron does not droop with the linkage disconnected.