750XL
What you describe sounds entirely credible. Some airlines are well aware that LGW is stretched for resources on a normal day and is not the best place to divert to unless it is the only alternate you can reach (fuel).
FWIW if we are headed for LHR we will usually have LGW as our nominated Alternate on the Flight plan but if a diversion is on the cards and obviously only if our fuel state allows then Stansted or Luton are the better options, simply because they are more "friendly" from a customer service/refueling/onwards travel point of view.