10 years ago there was USAirways and Continental, and Northwest a little before that. Reduced competition buoys the remaining survivors, but the history of bankruptcies in the industry certainly lends quite a bit of doubt towards your assumption.
Crazy to think JetBlue wanting Spirit. I remember when JetBlue started, their goal was to provide a better experience than all the other airlines. It is really a cutthroat business. Virgin Airlines had to be folded into Alaska too.
https://www.cnbc.com/2017/10/18/branson-says-alaska-air-was-...