I've never seen any catchment area figures for Irish Airports, so I cam up with some crude ones of my own based on where I thought you could drive to in a certain timeframe and the population of various electoral districts.
The figures I got were
Cork
Within 1/2 hour: 310,000
Within 1 hour: 500,000
Within 2 hours: 1,030,000
Shannon
Within 1/2 hour: 180,000
Within 1 hour: 410,000
Within 2 hours: 960,000
So, the differences aren't that big between the two airports, although Cork has a lot more people who live very locally.
Obviously, there is a huge overlap of people who live within 2 hours of both airports.