Droghwings,
You make a lot of sense and the parallels with the Cork scenario ring through.
However, while 1 airport for Belfast makes sense, and I agree a coherent aviation strategy is needed, both airports have massive price tags over their heads. The only way to move to 1 would be a merger.
This topic was the subject of fierce debate on this thread for some time and there prevailed distinct groups for and against each airport.
I suggest that having easyJet up at BFS offers a certain level of protection for carriers at BHD namely EI and BE. We can be sure if all operated from the same airport , EI wouldn't have stuck out on LGW and BE wouldn't be serving many of their domestic routes except for thinner ones like CWL ABZ INV SOU LBA and EMA.
This is if course hypothetical and nothing much will change. It seems that this limit of ops at BHD will keep EZY where it is and Jet2 due to its Canary Island routes will also stay put. Yes EasyJet did try BHD but I view their assessment of BHD as flawed !!!