I think flexibility in the aileron is of secondary importance and should not be the cause of the problem...

In essence, with the control locked and you force the surface, the top of the surface at the horn point should do exactly the same as the bottom of the surface...

This is achieved one of two ways, a good plate locked into the ribs of the aileron front to back, or a good plate that is attached solid through the aileron to the other side with no gaps in between. with th epower of todays servos and peoples attention to descent control rods, and hopefully control horns (not always !!) the bit that sometimes gets forgotton now is the need for strength and weight distribution in the surface... a chain is as strong as the weakest link and all that !