True Blue
I think your assessment is reasonably accurate, the load factors on the new routes to the Med & Gran Canaria have been very impressive and as you say often sold out and we have yet to hit peak UK summer travel period, the number of based aircraft increases from 3 to 4 from July into August, but based aircraft are only part of the picture due to the large number of flights that start elsewhere including AGP/ALC/GCI.
The surprise routes have been some of the Northern Norway routes like Tromso, until you factor in that it only takes a little longer to fly to LGW than OSL and London is cheap, very cheap when compared to OSL and this route will now operate year round.
It won't fail as a base, in part because as you pointed out it already had a good volume of scandic routes, customer feed back is excellent, it seems a combination of allocated seating, new aircraft, free wifi and very few delays or cancellations together with very aggressive pricing are getting bums on seats from where yield management can start to come into play, only gripes i have heard are that some flight timings could be better and the on board food is a little pricey.
Just who they are taking business off remains to be seen, the growth on OSL & ARN suggests leakage from LHR, the BA turn back en route to OSL (engine cowls unlatched) had only 75 pax on board