I'v e never seen one bent or broken but I imagine that any degree of abuse is possible. Because the rear case cover is a casting, I would assume (maybe wrongly) that the casting would fail before the shaft would.
The only 'preconceived' notion is what the op listed, nothing more. Not sure where you came up with that comment but it don't hold water with me.
The output end is heat treated , case hardened and stress relieved (normalized) so breaking it would entail a fracture, not a twist. I'd sure like to see a picture of a twisted one, do you have that or is that conjecture on your part?
Not here to argue, just present the facts and the not so apparent cause as I see it and I'm experienced with tear down and replacement of components having done it before.
Not a peep from the OP that I can see, neither on here or on OTT and I just looked about 2 minutes ago.