"There is a school of thought that Jet A1 fuel cannot reach the temperatures required to melt steel unless supplied with excess oxygen."

Please realize that steel fails long before it melts. The melting temp is not a factor at all. What needs to be looked at is the temp at which the steel fails to perform under the load that is required. I sold industrial metals for 16 years and I doubt that anyone ever asked what the melting temp of a metal was that I sold. Performance during stress tests - yes. Melting - no.