Surely all BACX pilots are the ones who are sub-contracted? i.e. they (and BACX) are doing work that was originally done by BA. BA were too expensive, so BA sub-contracted it out to a cheaper subsidiary.
The result of this is that the proper BA pilots should have the first choice of what work they want and where they want to work from. The sub-contracted guys (i.e. BACX pilots) should join the back of the queue and recognise the rights of their more senior colleagues.