Ex EU flight from DUB most definitely works from DUB, ive done a couple myself on AA.

There is the advantage of clearing immigration at DUB, but it does mean changing plane at either PHL, ORD or JFK, not ideal if you are going to SFO, but since AA don't fly from LHR to SFO you have to change somewhere.

At all costs avoid the 757 on the overnight flights, which is always JFK and PHL at certain times of the year.