I haven't followed the story over the years but I have seen nor long ago that they were looking at imperfections or cracks in the composites. Now you say corrosion.
That rudder input thing always struck me as bogus. If "aggressive" rudder inputs can rip the tail off THAT easily the ground would be littered with fallen planes.
Remember that the control surfaces must acutate or stop movement of a known mass at known velocities in the air. That deflecting the rudder of a plane in that particular plane's configuration, even sharply, can knock off the tail just doesn't pass the laugh test.
Ask your instructor what it would take to rip off the tail of a Cessna 150. It can be done easily BUT then extrapolate the speeds and forces involved to THAT JETLINER.
For all I know composites are fine but I suspect something was wrong with that particular plane.
I think it was the attaching bolts that failed. My instructor said you could rip the tail off by using heavy rudder inputs when turning to final if you do a heavy side-slip to get down ....