Brilliant - Train-Luas-Train takes "multiple modes" or drive for just over 4 hours, but according to you one can "pop" to Cork or Dublin Airport - by the time you've driven up to Cork Airport you could be at the tunnel on the road to Belfast or well ensconsed in Kent Station and availing of their refreshments.
Door to door timewise Cork City centre to Belfast City centre is quicker than door to door Paris centre - no matter how much you'd like to present one as a trip by "multiple modes" while the other is merely a "pop" to the airport and you're magiced away to Paris centre. You have to be in Cork Airport nearly 2 hours ahead of a flight to Paris, then it's another 90 mins on the plane (sometimes less) then it's a train taking the bones of another hour into centre of Paris.
You seem to think that drive/taxi-flight-bus/train is easier than drive for a shorter time or travel by train-luas-train which of course is cheaper too.
GoWanYaLanger!