Jetmagic did operate to Brussels - twice daily at one point.
As for the Amsterdam claim, as a former heavy user of the ORK-AMS route, I can give some anecdotal evidence.
Judging from what I would see in Schiphol train station, I reckon 10-15 people a flight were getting off and taking the train to Antwerp or Brussels. That's quite a chunk to lose in terms of viability. What's more is that they were often the business travellers who would be flying every week and not paying rock-bottom fares.
I don't think it's possible to get stats on usage, but I would imagine flying to Schiphol and getting the train down is currently the most common way to get to Brussels. Some will fly to Paris and get the train up; some will connect in London; some will fly from Dublin, so various routes get slightly affected, but I think ORK-AMS would be the most heavily affected.
On a side note, I would personally prefer Frankfurt to Brussels as a new route
- It serves an area that is currently tricky to get to
- It offers connections that aren't available from LHR, AMS or CDG
I've had to travel to Austria (Graz) for work a number of times lately and that has effectively meant overnighting in Dublin before the early flight to Frankfurt.
The problem is that it would only really work with Lufthansa overnighting a plane and when they're not serving bigger airports like Bristol and Newcastle, which also have more business users, it's hard to see them opting to do that in Cork.