My point is airlines and routes come and go from SOU, and the view on this thread is consistently that it's the airports fault for not investing, or the airlines fault for not advertising, etc, etc
These repeated comings and goings would indicate that the routes that have operated are marginal at best. There maybe one or two odd airline choices, but this seems to be a consistent pattern at SOU. Airlines don't drop profitable routes for no reason.
Maybe the airport just is what it is - it is constrained by its location, and has LHR and LGW on its doorstep.