LTNman
As you say, no one on here knows the economic success or otherwise of the DUB-SEN during its period of operation. I'm not sure if its market was entirely local as it carried over 6,000 pax per month but let's leave that aside.
If I had been advising Stobart I would have drawn their attention to the intangible benefits that the route gave to SEN. Namely a multiple-daily service operated by the Irish national carrier (as far as most passengers were concerned) to a European capital city, and offering genuine through connections to half a dozen US destinations ,thus 'proving' SEN's claim to be a true LON arrival/departure point. It also would be a useful fact to mention in discussions with other potential airline customers. In essence it gave SEN credibility to those that they are trying to convince of the fact.
Maybe the economics were so bad as to outweigh such considerations but I would be surprised if that were the case.