Well, I wouldn't diss Norwegian so fast.
Their operating costs are so low because they have a homogenous fleet that has a very low fuel burn. The maintainance is contracted out and of decent standards, otherwise the aircraft lose value. Pilots need to be paid industry wages or else they are gone, as there is a severe shortage of qualified pilots in Europe. If you take a peak at the pprune forum you will see that they also have hiring standards.
https://www.pprune.org/terms-endearm...n-updated.html
https://www.pprune.org/terms-endearm...lgw-based.html
Irreg handling at LoCos is defintely sub par and that is a clear case of 'you get what you pay for'.