You're right about the unique design of the WTC buildings, but that doesn't change the physics of gravity. Remember that a building is designed to handle predictable loads -- the mass of the building and its contents exerting downward forces, and wind loads and seismic activity exerting lateral forces that are typically very small compared to the dead load (building and contents) and live load (people and processes in the building) of the structure. Once the configuration of the building or its structural elements changes substantially (by leaning, for example), all bets are off and it will no longer behave the way it was originally designed.
I’m a civil engineer (structural), licensed in New York. Worked on the World Trade Center before (kinda trivial but the work we do) and after 9/11.
I would agree, the leaning of the building does indeed introduce a “secondary moment” as such, now just 6 inches at the top it’s probably still neglegable, but concerning.
I use to do a lot of work on steel transmission towers, hand analysis and computer analysis. Until that building approached about a 9 degree tilt, the secondary moment is arguably neglegable. NOBOBY will in that building when it’s tilting 9 degrees.