And you think Ryanair don't have anything to do with it???
Ryanair actually only have about 12 million passengers per year at Stansted now, down from 15 million in 2007 so Ryanair is not really that likely to be a reason for holding Stansted back. If Ryanair were growing at Stansted whilst the total traffic at the airport was falling, then Ryanair would be the one to blame, but Ryanair is just as much as a victim as all those other airlines which have been ripped off at Stansted, it's just that their operation there is too big to move elsewhere.
In a way, airlines are better off than they were 5 years ago (when Stansted had a good range of different airlines) as Ryanair have less less now than they did then. So I suppose yes, I think Ryanair has not got that much to do with the Stansted declines. Stansted has proved it can have the large dominance of Ryanair and still offer a wide range of services from other carriers.