What you are all talking about are crumbs. Even a moderately successful airport like Luton handles more airliners in 1 hour than Manston handles in a month. This must be very obvious to Manston Management.
With airports like Stansted and Gatwick losing flights left right and centre there are plenty of slots at these airports now.
Manston could best be described as an overflow airport except that even when there was a slot shortage at the major London airports airlines still stayed away. This has probably more to do with location, location, location.