PF - you have a point about Newquay. I'd also tend to agree with you that a 70+ seater out of Carlisle is too big an aircraft at the moment - something from Loganair seems perhaps a little more appropriate.
However, I maintain that if a city has not been able to maintain A320 / B737 service to an airport near London, then the number of people wanting to fly via Southend to Cumbria is likely to be extremely small, and should be substantially ignored when forming any sort of business plan about commercial passenger flights to/from Carlisle.