Shannon is Limerick's airport. Are you referring to Limerick as small or trying to cause tension.
Keep on mind that SNN has 3.7 mil pax a few years ago but only 1.7 this year. There is room for growth, TATL realistically make up little of this loss and a motorway to DUB doesn't steal 2million pax.
As for size it is small not trying to cause tension.
Your right about DUB not stealing them, Cork and Shannon were and still are heavily reliant on outbound numbers which have suffered in recent years and while increasing again it will take time. People are still selective on where they go and how frequently.
SNN busiest year was 2006 with just over 3.7 million passengers but started to fall right away even before the economy went down in 2008 which says a lot. I don't think you will see such figures again for a long time if at all.
Cork was growing up until 2008 and it's amazing that SNN had almost half a million more passengers and was the second busiest airport.