If I have my maths right, that is 140 per day. But 2013 was before destination like Aberdeen, Exeter, Guernsey or Belfast came online (not sure about the start of Isle of Man and Jersey). Not all of those are exactly easy to get to from the continent.
I have connected to DUS through LCY from EDI, GLA and IOM. For IOM, it was the only LON option, For GLA and EDI, I found the experience to be much better (and quicker) than the alternative, connecting through LHR T5.