and still people are demanding seniority
Actually in the last 3-4 airline take overs or mergers it is BALPA HQ and their lawyers that have pretty much demanded that whatever process was used peoples seniority was largely preserved. The reason given was that to do otherwise would likely lead to a legal challenge to the whole basis of the seniority system, something that BALPA did not want to contemplate.
Now the airline involved is BA the tune seems rather different. Are we surprised?