If I was a carrier looking at Cork, I would be very reticent about going in. Both Aer Lingus and Ryanair have a record of chasing out other airlines. Why would an airline establish a route only to see someone else take the profit? The route support scheme may need some kind of alteration to shield airlines opening up a route from that kind of behaviour.
For Iberia Express, the decision was easier. The shared ownership with Aer Lingus halved the problem.
Swiss are presumably assuming that Ryanair aren't going to touch Zurich and that Aer Lingus don't see the competition in such a small operation and the route as too thin for an A320.