Norwegian @ BHX
Looking back at the CAA stats Norwegian started BHX in March 2015 operating Madrid as the sole operator only for every man and his dog to pile on the route, Barcelona was alongside Ryanair and Monarch (seasonal at the time) and then joined by Vueling with Malaga having Ryanair, Monarch and Thomson all year round and then joined by Vueling and finally BACF.
Fares outside of the school holidays were light to say the least and thus the claim of poor yields seems reasonable.
Loads I would say that in general they fared better than Vueling (especially in winter) but the brand recognition (only a personal opinion) never really got established at BHX although those who tried them heaped praise on their product in general.
It was noticeable that it was before Monarch went under and Primera announced their impending flights that they hadn't any winter flights on sale and I assume neither had any bearing on their decision and it appears they were going come what may.
Did they make bad choices in respect of the routes they chose? This is a difficult question but with Madrid and Malaga and later Tenerife I would say no, as at the time there was enough spare capacity at BHX, although I would not say the same of Las Palmas which was short-lived and Barcelona they must have known that they were entering into a battle.
With Madrid they were just unlucky as who would have thought after years without a service, that IBS, FR and ZB would take it on in quick succession.
I think in the end it was over-capacity and even the Monarch loss could not persuade them to change their mind and obviously Vueling have come to the same decision as well (minus Barcelona which remains).
It seems it was just a case they came, tried hard, gave the routes time and circumstances changed to make continued operations impossible and they have moved on.
Maybe some lessons to be learned by BHX in respect of multiple operators on a single route but at the end of the day if an airline wants to operate and pay the fees it is unlikely that they will be turned away.