this article highlights that legacy US airlines created a business model well back during the deregulated era that was not conducive with investment grade ratings.
I have repeatedly stated and the article notes that better investment ratings combined with the total level of debt makes a big difference in the total costs for an airline.
DL's commitment to reducing debt, including pension debt, is the difference of what DL has committed to doing wholeheartedly differently compared to other legacy carriers.
as for WN, they never had defined benefit plans because they had problematic elements years ago....
as for AK, they have rapidly grown on the west coast which helped immensely to keep costs very low even though they are a legacy airline. Their low costs and high fares because they have dominated SEA are precisely a major reason they have done so well financially. WN has not been as far away from the legacies compared to AS but their success is due to some of the same factors.
the big 3 legacy airlines are all generating billions of dollars per year so there is no excuse not to transform their financial situations if they believe that is something that needs to be done.