For the sake of the guys that were fed 'assurances' at interview and subsequently, I hope that you are correct. But how can it be cheaper to run 2 conversions (necessary if promoting from within) rather than just the one for a DEC?
Of course all businesses are cost driven, but the smart ones realise that a little money spent now (for example on significant improvements to Terms and Conditions in line with inflation and market rate) will save a lot of money later by not having to replace pilots that resign to take better Ts and Cs at other airlines or leave in search of the very promotions that you speak of.
I agree with your sentiments - I just can't see it happening.