Quote - Some swing is necessary in the forearm, one should note, in order to un-bend the joint.

That is true, unfortunately. To get the arm perfectly straight, one has to use the swing. I apologize for the inconvenience.

ETA: That said, real arms do not tend to be perfectly straight, so one might argue that the "Attention" pose would be just as realistic, or even more so, without the swing applied.

-- I'm not mad at you, just Westphalian.