Valid point - if BA had been clever they would have removed the PSR from First and let the CSD work there and leave the PSR in Club to operate the galley as they have the experience! I agree that Nos 2 - 777 - and 7 - 747 - are usually the last positions to be chosen and it is not fair as they have not been given any adequate training.
One suspicion is to let main crew get the experience of running the galley - as it is probably only a matter of time before BA removes the PSR in First and has it replaced with Grade 1 CC.
My thought is that BA only wants 1 CSD and 1 PSR - to supervise WT - on WW.