Traditionally attempts at flights to the south east coast of England from Dublin have not faired well. Norwich, Manston and even Humberside never were popular. Clearly SEN has been the exception.
My suspicion is that the origin of most traffic on the route between Dublin and Southend originates in Southend. That coupled with the proportion of traffic going onwards to the US suggest that it could be more economical to market the route as Flybe with all other SEN routes.
May pave the way for BE to interline more with EI, feeding pax from CFN, INV, SOU, EXT and LCY through DUB to the US!