You neatly avoid this next point by simply ignoring it: If the floors in the falling upper block are crushing 'one floor at a time' the larger, more robust, undamaged structure below, then for each floor crushed by the upper block a floor in the upper block would also be crushed
. This means that the mass of the falling upper block was being reduced in mass by the ratio (in floors) of 1:1, ie. one floor per floor crushed below. I do hope you're not going to be foolish and tell us all again that Newton's third law action = negative reaction
doesn't apply in this case, as it clearly does. Given the bountiful visual evidence which shows very clearly large sections of the structure being turned to relatively very small pieces and ejected laterally then what sufficient mass remained to crush the rest of the building after all the falling upper block floors had been crushed by the structure below?