For a combined business that turns over very roughly between half and three quarters of a billion pounds a year (CX not BA) you can be quite certain that, in percentage terms , the cost of aligning wage scales and other Ts and Cs would be quite containable.
What has to be addressed either by the current board of BA( or their administrative receivers if they do not) is the profligate waste of a mangement structure which belongs to the last century.
That self same mangement also need to learn that a pilot is a pilot is a pilot. The fact that he is BA does not make him into a super hero with amazing value which makes him worth shed loads more than any other pilot.......
The solution is quite simple really for anyone who does not have a vested interest in not seeing it.