You are repeating what is - with respect - a common misconception. When you factor in the time taken to actually get from plane to train, Southend actually compares very favourably with other London airports - particularly if you are travelling to the City of London district. What leads you to believe differently? How did you fare last time you used Southend? Last time I arrived there - hand luggage only - I was on the station platform some 10 minutes after descending the steps from the aircraft.
Absoultely spot on and accurate, however you need to market the airport and as soon as you do, people see the word "Southend-(on-Sea)" and book elsewhere. It's a mindset thing, a quantifiable marketing behavior. Likewise,no matter how handy Prestwick is for Glasgow, it's still Prestwick and always will be in the minds of the travelling public. Only price can beat that mentality and you can't sell Dundee-London on price against easyJet from EDI.