I have always been a great believer in knowing your airplane. There is a distinct difference between nudging at the edge of the envelope to see how it really handles, and carelessly stressing the structure just for the hell of it.
The maneuvers described don't seem very dramatic to me so it has to be the way in which they were carried out. Bob Hover wouldn't end up with a bill for megga $'s after his breath-taking demonstrations. The guy that rolled the prototype 707 really didn't think that it was that big-of-a-deal.
Here, I know for certain that the BAC 1-11 and the Fokker lookalike have been rolled. All done without too many stresses and strains.
I have taken what was called ‘violent avoiding action' to miss something one day, and the 1-11 went past 90 degrees of bank. In fact, just for a moment, I considered carrying on with the roll as the smoothest way out of the situation. There was a socking great tool box on the floor, and it didn't budge. It was a strange thing, but when we were invited to try fast rolls during training (all done in the real airplane in those days) no-one that I knew, really pulled it round very fast. Fright is a funny thing.
I have also been in a storm for what seemed an eternity. Several time the horizon bar disappeared behind the top or the bottom mask. I wouldn't have expected the engines to all fail. Bl00dy glad they didn't, things were tough enough already.
I have also, in clear air over the Alps, gone down four or five huge drops of 1,000 feet each. It was like going down concrete steps. My jacket swung on its hook and almost reached the ceiling. So much for maintaining positive g. (There was a T-storm, well below us, 12NM to the West of our track.)
I think the point about gyroscopic effect causing unacceptable bearing loads, is the most lightly scenario. It still seems an extraordinary bill for just throwing the airplane around. Was there any airframe distortion? cos if not, it would seem that the engines/gearboxes are a tad vulnerable.