Yes, but don't forget that the only Flagship lounges within the US are at JFK, LAX and ORD. JFK and LAX are nice. ORD wasn't that special last time I was there, but that was a few years ago and it is still better than the other lounges there.

With regard to domestic US lounge access generally, this is often rightly advanced as an advantage of being BA silver or gold over AA platinum or executive platinum. But, access to the AA (and QF) lounges can be purchased with cash or AA miles. The price varies according to status, but for an AA platinum it would be $450 for the first year and reduces for renewals. There have often been promotions offering discounts of $50. Paid membership is more advantageous than status based access as it enables the member to admit up to 6 guests and there is no requirement to be departing on a oneworld flight (or any flight).

So, I think in many cases AA will be the way to go as probably the biggest benefit of BA can be bettered by spending £300 or so.