You are mixing up you dynamics. Washout is as you describe and is used mainly to reduce high speed tip stall. As an aircraft does a hard pitch the root stalls first quickly followed by the tips. With additional wash tip stall is delayed. A flap also used with subsonic speed manoeuvers also are deployed to camber the wing and delay stall.
But washout is not applied in all cases where as flapperons often are like of the F/A-18 or F/A-18 E/F that doesn't have washout but lands with flapperons. They land on Carriers requiring a high stall tolerence as they seek the shortest landing and agressive glide slope. They can be stalled as any aircraft can be but this isn't due to the fact that they use flapperons; it because they are being stalled unknowingly or intentionally.

In fact all a flap is doing is just cambering the air foil. A camber air foil doesn't stall because its cambered.

So you are mixing two different techniques used for different purposes to exclude the other. Washout by twisting the wing on EDFs at this Reynolds is not recommended as it can induce other issues. What works better is a thicker foil at the tip to achieve a similar washout effect.