Aer Lingus could make a fortune in Belfast if they just thought outside the box a little.
belfastmark
I would agree to some extent; in summer some markets could do well where the volume exists eg some of the Greek Islands and the 320 is a good size for this on a seasonal basis.
However, the winter is the challenge for a 320 with 172 seats in new markets. Milan is the example. some flights had less than 20 passengers and many of these probably at the lowest fares.