I think you will find that these days training costs are negligable once within BA due to the advent of zero flight time training. You will also find that BALPA have offered the company a zero cost option which is not good enough it would seem.
It is not zero cost if you consider the logic that I wrote above the quote of mine you selected. ZFT training is still a cost, and the consumate step up in the PP at which people would enter the mainline business is certainly a cost to the company.
Nevertheless that is not the relevant point as to why you would wish to challenge management on this project. You would challenge them on it marginalising you in the business if it is a success (unless it is flogged aswas GO).