Sorry BCN boy, Gatwick could take up the slack but the airlines you mentioned are only operating into Gatwick solely because they cannot get slots at Heathrow. Nobody wants to fly long haul from Stansted and there are very few long haul long flights - and some of them are struggling - from other airports in the UK with the exception of the Middle East carriers.
It is just a simple fact - everybody wants to fly in and out of Heathrow - simples!