It is never a great strategy to rely on every London airport being full first then hoping that Southend becomes airport of last resort. It won’t be happening next year, in fact I can see Easyjet consolidating services away from Southend, as a recession kicks in.
The sad truth is that Southend is not located in a great location even though it has a direct rail link. At the moment the airports share of London’s passengers is a fraction of 1%.