“I’d like to see a test of both arms extended against a single shooter in that case.”
To so that you have to be firing both eyes open and with the weapon(s) not in line with the eye. Otherwise they get so close together you can scrap up your hand with the opposite side pistol recoil.
Firing two at once as fast as one can be done, I think, but would take a LOT od dedicated practice. You have to be able to point shoot with either hand out of line of your head.
And even if you COULD do that, you lose your speed advantage as soon as you have to reload.
The difference between moving a weapon into sightline picture with the two arm technique shown with extend-retract-extend and moving from one extended sight picture to the other shouldn’t be a point of argument, frankly.
If you can’t see that I don’t know what to tell you other than look at the physical distance this guy moved his ‘dual pistols’ through. Did the single pistol extend-shoot-retract and then extend again?