What I still don't understand is how these aircraft are not overstressed,
and are able to keep control at all. I realise that this story is an extreme
example, but how about the "normal" flights? How do the planes survive?

Is it just because they are built to take the load factors?

Perhaps you are not a pilot and hence are not aware that if the plane
is flown at "maneuvering speed," the wing will stall before the stress
is sufficient to cause it to break.

vince norris