Pilots in general can only benefit from these aircraft being flown by BA pilots.
If BA pilots fly them, this means more (relatively) well paid jobs than if BRAL fly them. Maybe the prospects within BRAL would not be so good, but overall pilots end up better off.
It is really important that BALPA fight to keep these seats from going to the lowest paid bidder. How would you like it BRAL if your work was given to someone offering to do it cheaper?