TDLR: The building would have shredded the plane, and proper fire retardant system would have allowed the fuel to burn itself out in less than 2 hours with virtually zero structural damage to the building (superficial damage is NOT structural damage).

They intentionally monkeyed with the fire retardant coating on the targeted floors for one of the buildings to make sure there was a big fire:

In 1995, The Port Authority performed a study to establish requirements for retrofit of sprayed insulation to the floor trusses during major alterations when tenants vacated spaces in the towers [13]. Based on design information for fire ratings of a similar, but not identical, composite floor truss system contained in the Fire Resistance Directory published by Underwriters Laboratories, Inc., the study concluded that a 38 mm (1.5 in.) thickness of sprayed mineral fiber material would provide a 2 h fire rating, consistent with the Class 1B requirements. In 1999, the removal of existing SFRM and the application of new material to this thickness became Port Authority policy for full floors undergoing new construction and renovation. In the years between 1995 and 2001, thermal protection was upgraded on 18 floors of WTC 1, including those on which the major fires occurred on September 11, 2001, and 13 floors of WTC 2 that did not include the fire floors.

"Overview of the Structural Design of World Trade Center 1, 2, and 7 Buildings", NIST; https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=910105

Did they hit the wrong floors on WTC2? The intended targeted ones likely had the thermal protection also modified like WTC1.

Both towers designed to withstand the impact of an aircraft and associated fires due to impact of a B-25 bomber airplane into Empire State Building in 1945: https://en.wikipedia.org/wiki/1945_Empire_State_Building_B-25_crash

Design of World Trade Center Towers: Aircraft Impact

The structural engineers on the project also considered the possibility that an aircraft could crash into the building. In July 1945, a B-25 bomber that was lost in the fog had crashed into the 78th and 79th floors of the Empire State Building. A year later, another airplane crashed into the 40 Wall Street building, and there was another close call at the Empire State Building.[116] In designing the World Trade Center, Leslie Robertson considered the scenario of the impact of a jet airliner, the Boeing 707, which might be lost in the fog, seeking to land at JFK or at Newark airports.[117] The National Institute of Standards and Technology (NIST) found a three-page white paper that mentioned another aircraft impact analysis, involving impact of a jet at 600 mph (970 km/h), was indeed considered, but NIST could not locate the documentary evidence of the aircraft impact analysis.[118]

https://en.wikipedia.org/wiki/Construction_of_the_World_Trade_Center

Note that the 707 was a smaller version and earlier derivative model of the planes that supposedly hit with similar structural construction as a largely aluminum skin attached to minimal 7000 series aluminum frames and spars.