I don't know whether aluminum or composite would resist fire damage better, but it's not as simple as looking at the melting point of aluminum
As you say, not a simple answer.
One area AL
may have proved better here is it is a far better heat conductor. So if / while there was a relatively "small fire", the AL skin will conduct away the heat and keep the skin temperature lower.
IIRC the Boeing Tests seen elsewhere were not looking at this aspect, but a blowtorch concentrated on a small skin section. I wonder if that was as realistic as some of the "battery tests" they did?
amicus' thoughts / papers as ever discuss at length...