Cumbria is one of the most sparsely populated counties in the United Kingdom, with 73.4 people per km2 (190/sq mi
Has nothing to do with Southend but this route to any London airport with the same Southend landing fees would be a tough thin route.
There is an hourly train service that takes on average 3.23 minutes. Factor in the train travel times from London to Southend and then the check-in time the time saving would be just over an hour.