Just remember that AS doesn't have to cover the overhead costs of empty seats when they sell a ticket, but AA does.

If code shares work the way I think they do, then AS has a fixed cost for each seat they sell. Their profitability on the flight is very straightforward: Ticket Price - Negotiated Seat Cost.

AA's ultimate profitability on the overall revenue for the flight / cost of operating the flight. This can change rapidly with fuel prices, load factor, seniority of the crew, etc. Yield Management can at any time decide to change the available inventory of fares to reflect the current conditions, while AS can continue to offer the ticket at stable prices. Sometimes AA will be better, sometimes AS will be better.