Skilling said, "There would be a horrendous fire... The building structure would still be there." Furthermore, from the witepaper released by Skillings firm (quoted in
City in the sky: the rise and fall of the World Trade Center):
So, Skilling both personally and through his firm said the towers would not collapse due to slightly smaller and lighter but also notably faster jet impacts and the resulting fires.
Anyone can produce real world examples to show Bazant's claims of
crush-down before crush-up is pseudoscientific crackpottery until their arms fall off, while nobody will ever produce even a computer simulation to support Bazant's nonsense, as it stands in flagrant violation of Newton's third law. If you believe you need a paper to explain that to you further, you can't rightly be expected to understand it anyway.
The USGS found the iron rich spheres in the dust they collected just days after the attacks. As for your "other possible reasons" for the spheres, you might as well argue that they were planted by the devil for all the experimental confirmation one could ever rightly hope to produce in support of such notions.