I work in baggage at DUB and from what I have seen so far the level of transfer traffic is very small, unless alot of people are travelling without baggage?
I doubt many, if any, are travelling onward to the United States with no checked baggage.
Aer Lingus need to up their game in the United Kingdom with advertising their flights to the US. I'm not talking Press Releases; they need to advertise their US destinations on billboards, radio, side of busses etc to really get the message out there.
I have only come across one person who is aware of EI’s onward connections to the USA.