There is no more basis to believe that AA has a case to cry foul than it was when the DOT ruled in favor of AA/AS' private transaction. DL's request was denied, just as AA's would be if it tried to interfere.
Further, if the DOT decided to require that UA or DL could not obtain more slots - and it is far more likely it would be UA at EWR given they have a much higher share - they would not be looking to give slots to AA. The DOT and DOJ has shifted assets to increase competition; AA is in the JFK market and has given up size relative to its peers because of AA's own failure to compete in the market and AA is smaller today at JFK than it was in the past.
Further, it is highly possible that DL might not really care if the deal falls thru because it was UA's fallback to try to get something out of its departure from JFK. DL will undoubtedly give up fewer slots at EWR than it will gain at JFK and the reason why analysts recognize that DL's competitive position won't change is because DL is already the largest carrier at JFK based on multiple measures including flights, seats, ASMs, and revenue.
and DL has said that it would use the slots to increase capacity on its JFK-SFO route, using 767s as it does to LAX. Let's remember that some of the same people who are crying here about AA having a case to appeal for the slots were CONVINCED that DL's JFK-LAX 767 operation was temporary - because they were brainwAAshed into believing that 767s couldn't profitably operate on the transcons. DL apparently not only agrees on JFK-LAX but believes it can do the same to SFO using both the largest aircraft in the market but also by serving the cargo market which has no passenger carrier serving it. IN LAX and SFO, DL will be adding capacity which allays competitive fears that DL will be hoarding slots and reducing capacity.
Given that AA's own slot sale/lease allowed VX to enter EWR, UA could well see this move as a means to put the pressure on AA. which will be further pressured in the NYC market as DL and UA both grow and as AA potentially has to defend its transcon market from both LGA and JFK.
Let's not rule out that UA did this transaction because it knows that longhaul domestic flights are coming to LGA - which AA has said it is not supportive of any longer. Not only will DL have the largest transcon operation at JFK and UA will at EWR but DL has the ability to start LGA transcon flights and still serve the local NYC market from both airports.