The problem for AA and US as standalones remains that both have lost so much ground in key markets and are surrounded in key markets by DL and UA who AA/US say they need to compete with.
AA is slugging it out in ORD with UA who continues to make gains on AA despite UA's operational problems, AA has given up huge amounts of share to B6 and DL and now there is a real chance that LGA might well be one of the markets where the DOJ seeks divestitures, US is boxed in on the east coast by rivals in larger markets, and AA/US have both lost ground against competitors in the west.
AA/US have no choice but to merge at this point which is precisely why the DOJ is talking tough.
WN will bid higher but let's also remember that AA/US would rather not give up slots to low cost carriers flying mainline jets because the impact to AA/US down the road will be much greater. They would far rather give away slots to markets that only can support RJs. The chances are the DOJ will look at a combination of both types of markets but WN undoubtedly does realize that this is their last major chance to get significant amounts of slots at key east coast airports - and they aren't going to let the opportunity pass.