You'd have to think that they could have launched Shannon-Eindhoven if they wanted to hurt Aer Lingus in Cork.
In addition, any Shannon-Amsterdam route is likely to strip out the low-yielding leisure passengers, rather than the connecting passengers and business passengers who make up the majority of Cork-Amsterdam traffic, so the financial impact on Aer Lingus could be contained.
The sensible use of Amsterdam slots would be to go head-to-head or routes that are served several times a day by a single airline. That's where the best yield will be obtained.