Thanks for the replies above. Following up:

The routings I looked at were DUB - PHL - LAS out, PHX - PHL - DUB back, all in Business (or first on US domestic sectors).

My main aim is to save money and fly business. BA from GLA (where I am based) would normally net me 320 tier points on a J booking (140 on transatlantic, 20 domestic, x 2). The avios are less important as I have 300K, although I would still like to get as many as possible!

So if booking on AA on route above, would I receive less TP and Avios compared to a regular BA ex GLA reservation? I could possibly route one leg via LHR, i.e. DUB - LHR - LAS or PHX - LHR - DUB, although this impacts cost to a point.

Appears I have raised more questions than answers! All help much appreciated.