Human Factor.
I think you're correct, that would be one way of solving the problem. However would that mean that we 'lesser beings' would be admitted to mainline BA? Including those who've already 'failed' BA mainline transfer-in selection? You are correct for sure in one respect which is that a precedent was set when CityFlyer was absorbed.
Only other alternatives I can think of would be:
1. to add another aircraft type to BACX to absorb the surplus
pilots.
2. Lay some people off
3. Dramatically overcrew the existing a/c
4. Send the secondees back to mainline.
5. Something really clever from management which will do a sort
of 'Abracadabra' and 'POOF!' .....we all live happily ever after
Like I said. Glad it's not me who has to fix it. Here's hoping it ends well.