I do not agree you should move your arm much. Most of the action comes from the wrist.
You can disagree how much you like. Think that we are not like some heavy metal wierdos, who even want lock their palm to get most out of a single string speed haha.
With a strap you can even let the elbow joint move if you want. But the basic campfire strumming needs definately that forearm moving and rotating for sure from elbow joint.