We don't have times yet, so it's true that it, or another route, could be a W from Dublin. However, I couldn't see the logic in operating a W from Dublin into Cork at pretty much the same times as there is another aircraft operating a W from Cork.
I don't think you could squeeze out the required times from existing Cork schedules. You're looking at 5 hours that you need to get back. It's true that the AMS gets back quite early in the evening and the Heathrow leaves quite late in the morning, but those are decided by slots at those airports. And you'd still only find 3 hours if you took that to extremes. If it was year round, you could find spare capacity in the winter though.
Your last point about switching SNN-FAO or SNN-AGP to a 757 may work.
I looked at the fares out of Shannon and EI-A330-300 is right. AGP is weaker than FAO there. Whether that means AGP gets withdrawn or FAO gets a capacity increase from moving to a 757, we can see.