The wash-out is there to allow aileron control into the stall. Without it the aircraft had a vicious tendancy to end up inverted in a full stall.
Its a long time ago but as a QFI on the Dakota, I was always a bit surprised at the viciousness of the wing drop when stalling the Dakota with flaps down and approach power (around 15 inches manifold pressure). It was instinctive to use instant aileron and rudder to stop further yaw and looking back I wonder if the initial fright at the rate of wing drop and thus using aileron without realising it for a few seconds, exacerbated the wing drop. I recall a height loss of at least 5-800 feet before level flight recovery was effected.