All EasyJet can say is that the catchment area overlaps with Southend. I'm sorry but I don't buy that, there is no way the 3 aircraft and 10 daily flights they now have at Southend damages Stansted this much!
I know damn well why they are doing it! It's because they are doing everything they can to get the very best out of their new Southend base
Contradiction? You should iron out your argument before drafting that letter to them. Bear in mind that they wouldn't want to destroy their Stansted base just to help Southend - they'd probably only lose money via that strategy. What you'll probably find is that these cuts are temporary and they will want to come back to STN after a new owner emerges; then they can get lower charges/fees and make more profit.