[Anthem]

-- The external lattice frame that was used in their construction was an innovative design element back then, and I suspect the buildings would have stood a much better chance of surviving the impact and fire if they were constructed with a standard internal column/beam frame.

That's the standard story. In Jones' work he shows the bearing capacity of the internal column structure. In fact the building structural design is more redundant than most other buildings.

[Alberta's Child]

The external frame provided more redundancy, but it also provided more exposure to damage from external forces. I also suspect that the enormous size of the floor slabs and long horizontal distance between the core and the external frame made these floor slabs the weakest part of the structure. In a traditional building frame, it may be possible for individual sections of floor slabs to fail without bringing the entire building down -- or to at least cause the building to collapse in a slower fashion.