If you go back to the late Go/easyJet days (2001/2002) BRS and NCL were similar airports in terms of size and range of airlines - from memory pax numbers were very similar.
Since then they have diverged, based largely on the relative success (or otherwise) of the regional economies.
The fact that NCL has attracted Emirates and United, and also has slightly stronger links to European hubs strengthens the argument that it is BRS proximity to LHR/BHX that is impacting on long haul growth (though the physical constraints also play a part), because in most other aspects BRS has powered ahead (OK, maybe not in football related traffic
)