Picking two airlines is in no means random because which two you chose can and most likely will have very different outcomes.

As folks are mentioning ALPA merger policy will cover two carriers that are ALPA but as soon as one airline isn’t ALPA then it will change greatly. As in American-APA, and Southwest-SWAPA. The most recent being AirTran and Southwest. Ask them how that went.
And American doesn’t have the best history of being fair, to anyone other than AA pilots.