I think Stansted is a definite winner, if you look at other airports like BHX, they have ZB, BE, FR, TOM, TCX, VY and now Jet2. Similar at many other airports they operate from incl. MAN and EMA. When you compare that to STN there isn't actually that level of competition. What they will have to go up against to some degree is a dominant FR, but with the right mix of routes and different dynamics (i.e: Jet2 Holidays) in my opinion would be good entry point for the SE market incl. London.
They also seem to be heavily in the media (on TV that is) down here in the south. Maybe it's about time?