I don't think that is the point here. BA inherited the bmi position I.e. Ops at BHD, EI being already in situ meant that BA had to compete at BHD and rightly so, they'd be unlikely to go up to BFS and hand over the business to EI on the well established BHD LHR route. Now all of that has changed, BA now is in a very different position.
We could debate why any airline is at any airport in Belfast, there are specific business rationale for each, like eg easyJet not seeing ' any tangible benefit' from being at BHD... (though I don't necessity agree with their assessment/ findings).
It is of no consequence to me whether they fly from BHD or BFS.. I use BA frequently and incidentally live closer to BHD. My perspective is about giving balance this very one sided debate. It is a competitive market place. Whether BA move or not they'd be stupid not to assess the options...
There have been multiple rumours of various airline staff visiting the competing airports, some resulting in moves, and some not..
BA investigating a move to BFS is completely plausable. Given their position of relative strength, they could move and maintain their customer base in my view. For the business traveller particularly BHD is an excellent option, but they would have little choice but to follow BA if they moved. That's the point I think that needs to be considered.
EI-BUD