Jet2 is doing well but look at the routes they serve. Both EZY (except STN/BRS/BFS) and Jet2 are now just bucket and spade competition for the holiday charters.
NCL seems to be slipping back to where we were 20 years ago, capitals served by the expensive flag carriers of those countries and the charter holiday traffic to the med. Lets face it, what you have to pay these days to fly with EZY or Jet2 out of NCL it can hardly be called cheap.
You just have to look at the prices to go the same places from EDI, LBA or MAN and you will see exactly what I mean.