Where are the ulcc going to get the pilots to grow? If the economy stays alive and the legacies don't have major issues they are going to need 5-10000 pilots a year at the big 6. The regionals are the first domino to dissappear but it is a major issue going forward. There aren't enough pilots. If they do find a pilot to hire who is going to be sitting next to you in 5 yrs?
The LCCs took a few years to match the legacies contract wise and those dollars were compounding in the market while years ticked away. The great thing about a legacy is the goldilocks differences in flying. Widebody fo is attractive to some while others take the early upgrade. You can make more as a senior fo on a narrow body quicker compared to lcc where everyone is on the slow slog up the same aircrafts list. United has almost double the widebodies of American but both have a lot of debt.