Cork runway is far too short for the A321NEO, Norwegian couldn't get a commercial load out of Cork due restrictions (well the were hardly pushed by demand), the MAX would have been a bit better but still leaving empty seats. EI will stick with SNN/DUB and pre clearance.
The Aer Arran vs Ryanair face off back 15 years ago was a smash and grab job by FR who bled Aer Arran until they gave up as they couldn't make money. FR gave up quickly afterwards as they couldn't compete against the new hourly train service and the M8 motorway. Yes there is business but anywhere you can reach from Dublin you can go via LHR a token AT42 twice a day might work but only if its for EI.
CFN/KIR are PSO and paid for by the Irish government under contract with Stobart and EI handle the front of house. These are covered by EU regulations due distance and lack of infrastructure. Cork never qualified and Waterford, Galway, Sligo no longer meet the threshold due improved rail and road connectivity