The whole debate about ROI scrapping the travel tax is a bit of a red herring in my view, it's more about perception than actual price comparison. I'm not sure much actually changes in NI with the ROI tax removed. The airlines ex NI limit capacity to a point where they make a good return especially in summer where fares are huge. I refer to non domestic flights of course.
CO didn't increase capacity when the adp was reduced on long haul... Yes maybe they maintained better winter frequency but no other scheduled services started. The fact that DUB has such a wide range of services, passenger who book early are bound to get a half competitive deal.
Finally, as I've said before complaining about passengers going across the border to fly, this is nothing new, and Wont change. The main reason being passengers have next to no routes to Europe ex Belfast, there are literally a dozen over lapping routes, and on these carriers have limited capacity, so in my view the removal of the €3 tax is highly irrelevant...