Completely agree with you, Justin. If for a Fast unit doing Attack+Move or Move+Move Reactive Fire only takes place after it has done EVERYTHING, then it's not really reactive fire, is it? You would be a moron to waste your activation on a roll of the die, when you could just wait for your turn and then do a sustained attack.
I'm baffled by this response by FFG. It's just nonsensical. I hope I'm able to get a second opinion on this...