Not all new orders at AA are replacement. The order was perhaps 460 aircraft and adding up the S80 and 75/76 fleets, some of those Airbus and 737 orders are indeed for expansion. The 777 orders especially are for expansion along with the 787 (primarily destined for ultra long-haul that are not done by 767 or any other aircraft). Since pre-merger widebody opportunities will likely be a consideration, one could expect the pre-merger fleet plans to be an issue.

The argument for SLI purposes of what mainline (be it AA legacy, East or West) would have done is speculative and it's tough to say how the arbitration PANEL will weigh that component suffice it to say that at least in the UAL-CAL SLI, both the pre-merger situations of the carriers was considered as was fleet composition, which included both orders and options.