It's not so much the number of flights as the passenger mix. AMS probably carries more non-EU passengers than any other route. That slows up processing as the non-EU desk will process EU passengers when nobody is waiting (which is pretty much the norm on bucket and spade flights).
I presume the other flights were Stansted, Birmingham and Manchester?
Manchester also has its fair share of transfer passengers.
It is a bit of a pity that they can't find some way of splitting the arrivals so that Common Travel Area passengers can be separated and kept out of the passport queues altogether, however, it would probably be too operationally restrictive in an airport the size of Cork. It would also mean investing in some buses...