...The Flagship lounges are materially larger than the Polaris lounges with better food and drink. UA is a larger airline than AA with more INTL business class seats and yet they chose to build smaller lounges that are less well appointed for those people. ...
Are you sure about "materially larger", there are certainly fewer domestically (4 vs 6 ) and UA is enlarging ORD. Both AA/UA have plans to add another lounge (AA-PHL, UA-DEN)