– “The North tower collapsed in about 13.8s total which equates to around 2/3 freefall, total freefall being approcx 9.2s for 1365ft. Still way too fast.”
Yes, the internal collapse accelerated at around 2/3 of g, so 1/3 of the entire potential energy of the structure (before collapse) was available for destruction of materials.
Convert that to TNT equivalent and you can see that it was way more than enough.