Freight flights into LHR have boomed recently, whereas LGW has seen nothing, so there's more to it than slots.
Surely you recognise that slot availability is an overwhelming factor determining freighter activity at LHR and LGW? The current period is exceptional in that regard. Has LGW even been fully operational in recent times?
So those airports with existing infrastructure to handle large freighters have seen more, and those that don't haven't - not rocket science is it?
Hence my questioning of whether the wilful run down of MAN's capability in this respect, against the best interests of the region it serves, is something which needs to be reviewed. That isn't rocket science either.