IMO if you do not exclusively buy and travel on Biz/First fares, AA/AS is better than CX for FFP. As an AA/AS elite, you get access to premium class on AS and Main Cabin Extra on AA, which would take away a lot of pain traveling on domestic Y. Depending on the route, you might even get an upgrade to F. Lounges in the US are generally not that exciting, and the lounge access benefit is purchase-able either through an annual fee or a premium credit card, anyway. I don't think it's a huge deal.

If you do fly on Biz/First a lot... I would recommend you look into the BA program. Similar flavor as the CX Club Point system, but it's slightly easier to get OWE. Also, you get access to Main Cabin Extra on AA with BA OWE