Mart901,
I don't think it's a clean cut case of saying;
'IAG would gain literally nothing by moving operations in fact they would lose the current advantage they have in landing closer to Belfast than ezy/be, time is of the essence in business'.
There are competing variables in this equation, take the 2130 curfew for example, this means potentially that there is one less rotation with an aircraft each day. That is a real fixed cost for aircraft related to the BHD operation, compare to EDI or GLA LHR routes for e.g.
Yes there is that issue of exposure to EZY and FR competing services, but you have to ask yourself, with the large IAG combined reduction from 10 daily to 7 daily, just how great is the BHD attraction over BFS? Not preferring either (though I admit using BHD is very pleasurable), what extent of transfer pax are using the route? MAN LHR was previously 75% and GLA/EDI 50%. If the level of transfer pax is so high , aside from KLMs token service, not much risk.
Bolt on to of that the contracts that EI and BA have with corporates, to me , such a move would not be high risk. Equally, given the steep charges at LHR, point to point pax will always find the other London airports significantly more economical anyway.
Not proposing to conclude such an arguement on here but this debate is far from proven, equally easyJet's assessment that 'there were no tangible benefits of using BHD', was far from a comprehensive study into the matter, given that Ryanair were then at BHD, and EI had just launched at BFS, so holding their loads under those circumstances was a good result. Obviously we can't ascertain impact to yield though equally we couldn't forsee what it might have been at BFS..