If seniority didn't exist, they'd be a lot more movement between airlines. There'd no longer be a disincentive to move. Accordingly wages would be higher, for two reasons: (a) airlines would be offering higher packages to attract the right people; and (b) airlines would be offering higher packages to retain people.
Kinda like the rest of the world, actually....
Airline management secretly LOVE seniority, but they cleverly let us think that WE love it and never want to give it up!