Essexman -
I have only once flown into Southend, and I agree, from my seat on the plane to the front door of the airport took no more than 30 minutes. The slow part was to get from there onwards into London.
To get into the City of London from Dundee I would be amazed if a flight to Southend from Dundee could be either faster or cheaper than heading down to Edinburgh to fly into London City.