Well for a start they negiotiated Cityflyer cabin crew to fit in with seniority and rank with EOG cabin crew. Unlike Cityflyer pilots who went to the bottom of the seniority list.
You're not comparing apples with apples, I'm afraid. All BA pilots irrespective of their fleet or base are on one seniority list. Cabin crew aren't. I would imagine there would have been a mutiny had the Cityflyer cabin crew joined the main crew list and gone straight onto LHR Worldwide.
Having said that, BALPA negotiated an agreement to allow a number of Cityflyer captains to transfer to the 737 as captains even though their seniority was nowhere near enough. The only condition being that if they bid to leave the fleet, they revert to the same deal as everyone else.