Once fire weakens multiple individual structural members, collapse is both inevitable and rapid as the loads transfer within the materials to the remaining supports at the speed of sound.
You're assuming the fire would burn all the columns at the same rate at the same time, that's not what empirically is seen at other building fires.
For reference please google Grenfell Tower Fire. Or in China, the Mandarin Oriental Hotel Fire.
For gravity to be symmetric such that free fall speed is achieved by the whole building at once at the same time (start of collapse), all the columns would have to suffer the exact same fire made damage at the same exact time. I don't know about you, but i have yet to see nature produce exact results at the same exact time anywhere. Gradual, slow and chaotic describes nature better. Fast, precise and calculated usually is the realm of human beings.
Gravity is symmetric.
Once fire weakens multiple individual structural members, collapse is both inevitable and rapid as the loads transfer within the materials to the remaining supports at the speed of sound.