The airline gave you 4 months notice of a schedule change plus offered you an alternate flight albeit from LGW.
If flights were bought purely for the purpose of flying around, maybe the airline's actions would be acceptable.
But flights are bought to deliver people for holidays or other purposes and to cancel a flight and offer to replace it with a flight from a location 200 miles distant is very poor IMHO - shame on you Mutt for trying to make the OP look unreasonable.